We report a comparative study on the characterization of three trivalent uranium complexes using 12 density functional theory (DFT) methods, i.e., BP86, PBE, B3LYP, B3PW91, BHandHLYP, PBE0, X3LYP, CAM-B3LYP, TPSS, M06L, M06, and M06-2X, representing (meta-)GGA and hybrid (meta-)GGA levels of treatment of molecular systems. The MP2 method was used in single-point calculations to provide an ab initio view of the electronic structure. Three model systems in the experimental work on the activation of CO₂ and CS₂ by a trivalent uranium complex (Tp^*)₂U-η¹-CH₂Ph (Cpd2) were used i.e., (Tp^*)₂U-η¹-CH₂Ph (Cpd2), (Tp^*)₂U-κ²- O₂CCH₂Ph (Cpd3), and (Tp^*)₂U-κ²-S₂CCH₂Ph (Cpd4) (Tp=hydrotris(3, 5-dimethylpyrazolyl)borate). The hybrid functionals, B3LYP and B3PW91, displayed good performance in view of both the geometrical and electronic structures. The MP2 method generated consistent results as DFT methods for Cpd2 and Cpd3, while provided an odd picture of the electronic structure of Cpd4 that may be due to its single determinant feature, leading to its capture of an electronic configuration of Cpd4 different from the one with the DFT methods. The use of a quasi-relativistic 5f-in-core ECP (LPP) treatment for U(III) in the thermodynamic calculations was supported by the calculations with a small-core ECP treatment (SPP) for U. Owing to increasing interests in low-valent actinide molecular systems, this work complements previous comparative studies, which mainly focus on highvalent actinide complexes, and provides timely information on the performance of 12 widely used DFT methods in studying low-valent actinide systems. It is expected to contribute to a more sensible selection of DFT methods in the study of low-valent actinide molecular systems.

Using the pseudo-potential plane-wave based on the density functional theory (DFT), the electronic structures and optical properties of intrinsic ZnO, Y-, Cu-, and Y-Cu co-doped ZnO were studied. The results show that the conductivity of ZnO can be improved by Y and Cu doping because of the increase in carrier concentration under the order of magnitude of the doping concentration in this paper. Y-Cu co-doping leads to degeneration and makes ZnO metallic. Y-doped ZnO can show enhanced light absorption in the ultraviolet region, while doping with Cu enhances absorption in the visible and near ultraviolet regions. Y-Cu co-doping greatly increases the absorption of visible and near ultraviolet regions owing to the synergistic effect between Y ions and Cu ions, which can be exploited to fabricate the opto-electronic devices.

We employed the generalized energy-based fragmentation (GEBF) approach to investigate the gas-phase structures of B-DNA double-helices up to 10 base pairs at several theoretical levels. By comparing the results obtained using the M06-2X functional and other methods (including the B3LYP, B3LYP-vdW, and TPSS functionals), we found that the absence of stacking interactions could lead to the enlargement of the vertical distance between adjacent bases. The magnitude of this enlargement of the vertical distance quickly decreases as the length of the double-helix increases. The gas-phase stabilization of the double-helical structure of B-DNA is a cooperative effect, in which hydrogen bonding plays a more important role than stacking interaction does up to 10 base pairs.

The most stable (Al₁₆Ti)^n± (n=0-3) ions were modeled and optimized using density functional theory combined with all-electron spin-polarized calculations. The geometries, stabilities, and electronic structures of the (Al₁₆Ti)n ± (n=0-3) ionic clusters, as well as the adsorption structures and adsorption energies of H₂O molecules on the (Al₁₆Ti)^n± (n=0-3) ionic clusters, were studied. The results were compared with those obtained for pure (Al₁₇Ti)^n± (n=0-3) ionic clusters. The spatial distributions of the highest occupied molecular orbitals and the lowest unoccupied molecular orbitals for the (Al₁₆Ti)^n± (n=0-3) ionic clusters showed that the free electrons tend to occupy Ti sites. And a few residual free electrons would occupy sites with large curvatures. An extensive structure search was performed to identify the low-energy conformations of (Al₁₆TiH₂O)^n± (n=0-3) complexes. Based on the geometries of the studied adsorption complexes, it was found that the most stable structures were prone to oxygen-based adsorption onto Ti atom. (Al₁₆TiH₂O)⁺ ion featured the shortest average O―H bond length, that was ~0.0003 nm longer than that observed in isolated H₂O molecule. The O―H bond length increased with either increasing or decreasing number of the electrons. The studies implied that Ti dopant in Al ionic clusters improved the dissociation efficiency of H₂O molecules. Furthermore, the doping effect played a more important role than the geometry effect in determining the electronic structures of the (Al₁₆Ti)n ionic clusters and their interaction with H₂O molecules.

The coordination structures of metal string complexes (n, m)[Cr₃(PhPyF)₄Cl₂] (HPhPyF=N, N'- phenylpyridylformamidine; n=2, 3, 4; m=2, 1, 0) with potential applications as molecular wires have been investigated using the density functional theory BP86 method by considering the effects of an external electric field (EF). Herein, n and m represent the number of benzene rings on the left and right in the PhPyF- ligand, respectively. The results show that: (1) under zero field, the three kinds of coordination modes ((2, 2), (3, 1), (4, 0)) of the four PhPyF- ligands are close in energy, which indicates that they are competitive conformations. The (2, 2) coordination mode is the most stable one. The Cl axial ligands on the two sides of (4, 0) can coordinate to Cr atoms, indicating that these two axial ligands can combine with electrodes. Moreover, the Cl₄― Cr1 bond is stronger than Cl5―Cr3, different from (4, 0) [CuCuM(npa)₄Cl] [PF₆] (M=Pd, Pt; 2- naphthyridylphenylamine) in which the axial ligand Cl close to benzene cannot coordinate to metal atom M. (2) There is a 3-center-3-electron delocalization σ bond in the Cr₃^{6 +} chain for (2, 2), (3, 1), and (4, 0), but the delocalization gradually weakens. The polarity from Cl₄ to Cl5 is stronger as the coordination mode of four PhPyF- ligands becomes more consistent. (3) The geometry and electronic structure of the investigated complexes change regularly under the electric field. Because the electron transfer direction of (3, 1) and (4, 0) is the same as its molecular polarity, the bond length, spin density, charge and energy gap are more sensitive to -Z electric field. Therefore, the -Z elelctric field is beneficial to the conductivity of the molecules. Moreover, the sensitivity of the structures to electric field increases with polarity.

Molecular dynamics simulation was used to study the effect of the outer-wall on water flux in the inner channel by varying the inter-layer spacing of unconventional double-walled carbon nanotube (DWCNT) under reverse-osmosis conditions. Salt rejection and the water transport behavior inside the DWCNT were also examined. In the simulation, 0.5 mol·L^-1 NaCl aqueous solution was used to mimic seawater, and the chiral index of the inner-wall was fixed at (8, 8). A constant force on the salt solution produced pressure. Calculation of the number density profile of ions along the DWCNT axis showed that the water could be separated completely from the NaCl aqueous solution in some types of DWCNTs studied. Analyses of the hydrogen-bond lifetime, potential of mean force, and dipole moment distribution of the water molecules inside the DWCNT showed different permeabilities by water molecules and ions. An increase in the inter-layer spacing improved water flow in the DWCNT, which decreased the salt rejection performance. Finally, it was found that DWCNT with an inter-layer spacing of 0.815 nm gave the optimum balance between water flux and salt rejection. This study provides a molecular insight into the use of DWCNT in desalination, and will enable the design of improved reverse-osmosis membranes with high performance in terms of salt rejection and water permeability.

Density functional theory (DFT) and classical molecular dynamics simulations were used to study the effects of the interactions between zwitterionic alanine and some ions (Na⁺, Cu²⁺, Zn²⁺, and Cl^-) in saline solution on the association of alanine molecules. The DFT calculation results show that the association of alanine with these ions can enhance charge separation of zwitterionic alanine. Classical molecular dynamics simulation results also show that three associated structures of zwitterionic alanine molecules are present in alanine aqueous solution, and the associations can be weakened to a certain extent by the interactions between the cations/anions and alanine polar groups. The interaction between a cation and the carboxyl group of alanine can be greatly affected by hydration of the cation in dilute saline solution. The interaction between Cu²⁺ and alanine is much stronger than that between Na⁺ and alanine in the gas phase, but the situation is reversed in dilute aqueous solution, because the hydration of Cu²⁺ is much stronger than that of Na⁺. In dilute ZnCl₂ aqueous solution, the interaction between Zn²⁺ and the carboxyl group of the alanine molecule is less direct, because of the first hydration shell of Zn²⁺. However, indirect interactions between Zn²⁺ and alanine still lead to a decreased association among alanine molecules. In addition, the interactions of cations/anions with alanine not only weaken the association between alanine molecules, but also result in transformation between two typical conformations of associated alanine molecules. The ion concentration affects the conformations of associated cation/anion-alanine species, and associated alanine molecules.

Molecular dynamics simulations of oxygen molecules in NaOH and KOH solutions at different temperatures (25-120 ℃) and concentrations (1:100-1:5, molar ratios) were performed in this study. The interactions of oxygen molecules with the surrounding solvent and solute were clarified by considering the solvent-solvent, oxygen-solvent, and oxygen-solute radial distribution functions. The self-diffusion coefficients of the oxygen molecules and the solute were both determined by analyzing the mean-squared displacement (MSD) curves, using Einstein's relationship. It was concluded that at all concentrations, the diffusion coefficient of oxygen in NaOH solution is smaller than that in the corresponding KOH solution. The diffusion coefficients for hydroxide, Na⁺, and K⁺ decrease with increasing solute concentration, following similar trends to those of oxygen. The oxygen diffusion coefficient obtained in this study is in good agreement with the reported experimental value, suggesting that MSD is an attractive approach to study the oxygen diffusion behavior in strong alkaline solutions at elevated temperatures, which are experimentally extremely challenging.

The structures and spectroscopic constants of Zn₂ and Cd₂ were studied using the coupled-cluster theory with spin-orbit coupling based on the two-component relativistic effective core potential and matched basis sets aug-cc-pvnz-pp (n=Q, 5), combining complete basis set extrapolation of the electronic correlation energy and fourth-order polynomial fitting technique. Spin-orbit coupling was included in the post-Hartree-Fock procedure, i.e., in the coupled-cluster iteration, to obtain more reasonable results, although the spin-orbit coupling effect observed in Zn₂ and Cd₂ is not visible as it is in Hg₂. Our theoretical results agree well with the latest experimental values and other groups' theoretical results, and will be helpful in understanding the spectral characteristics of these two dimers.

ABaTiO₃ ceramic was synthesized using a conventional solid-state reaction, and sintered at 1400 ℃ for 4 h. The pure tetragonal phase was confirmed by Rietveld refinement of the X-ray diffraction data. The Raman spectrum and the far infrared (FIR) reflective spectrum were obtained and analyzed using Lorentz fitting and the four-parameter semi-quantum model fitting, respectively. The Raman and FIR spectra were assigned based on first-principles calculations, and consideration of the splitting of the transverse optical modes and longitudinal optical modes. All the vibrational modes were represented by linear combinations of the symmetry coordinates deduced by group theory analysis. Among the 12 optical modes, the Raman-active-only mode, B₁, can be viewed as the wing-flapping vibration of the O4-O5 plane perpendicular to the z-axis in the O₆ octahedron. The A₁⁽¹⁾ mode and the E⁽¹⁾ soft mode are split by the triply degenerate F_1u mode of cubic BaTiO₃, resulting in the ferroelectric property of tetragonal BaTiO₃. The appearance of the A₁⁽¹⁾ mode leads to crystal polarization along the z-axis and the E₍₁₎ mode causes the large permittivity. These two modes can be described as vibration of the Ti atom against the O₆ octahedral cage along the z-axis [A₁⁽¹⁾] and on the xy-plane [E₍₁₎].

The stability of anionic trans-dioxo manganese(V) corrole complex and the protonated species structure were investigated using density functional theory (DFT) with B3LYP method. The calculation results show that trans-dioxo manganese(V) corrole complex has one σ and two π orbitals in its O=Mn=O bonds, which are composed of the d orbital of the manganese atom and p orbitals of the two oxygen atoms. Enhancement of the electron-withdrawing ability of substituents results in a decrease in the O=Mn=O bond lengths, and shifts the O=Mn=O Raman stretching vibration to a higher wavenumber. On protonation, one of the axial oxygen atoms gains two protons and is transformed into a water molecule. The manganese atom then cannot hold water tightly to form effective coordination bonds with water. This results in irreversible protonation of the trans-dioxo manganese(V) corrole complex, which leads to formation of an oxomanganese (V) corrole complex.

Density functional theory calculations were performed to study the mechanism and reactivity of methanol oxidation mediated by Pt_nRu_m (n+m=3, n≠0) clusters. The potential energy surfaces and pathways of the initial O―H and C―H bond activations were predicted. The results show that the activation of methanol proceeds preferentially along the C―H bond activation pathway. The calculated reactivity order was Pt₂Ru>Pt₃> PtRu₂. Frontier molecular orbital analysis showed that the initial C/O―H bond activation is a proton transfer process. The solvent effect was also investigated. This study will enable a deeper understanding of C/O―H bond activation and provide new ideas for catalyst selection and optimizing conditions for methanol activation.

The magnetic properties of the antiferromagnetic complex μ-1,3-N₃-Ni(II)[LNi₂(N₃)](ClO₄)₂ (L= pyrazolate) were investigated using density functional theory (DFT) calculations combined with the broken symmetry approach. The calculation results obtained using the hybrid density functional theory (HDFT) agree well with the experimental data, and accurately describe the magnetic properties of complex. The large energy splitting, 0.93-0.99 eV, between singly occupied molecular orbitals indicates that there is strong non-degeneracy between them, and the two coupling paths (azido and pyrazolate) in the complex show that there is overlap between the p orbitals of the N atoms. All these factors contribute to the antiferromagnetism of the complex. The magnetic properties of the complex are also closely related to the dihedral angle τ of Ni-N-N-N-Ni. The antiferromagnetism of the complex increases as τ decreases from -55.38° to -1.5°; the maximum absolute value of magnetic coupling constant (J_ab) occurs at -11.95° (J_ab=-151.02 cm^-1). During this process, the coplanarity of the seven-membered ring, which consists of two Ni(II), one azido, and two bridging nitrogen atoms (N(4) and N(5)), is enhanced, i.e., coplanarity increases the antiferromagnetism of the complex.

Mechanisms for the [Fe(MgBr)₂] catalyzed cross-coupling reaction between ortho-chlorostyrene and phenylmagnesium bromide to form biaryl were studied using density functional theory (DFT) calculations. We investigated two mechanisms. Cycle A included three basic steps: (I) oxidation of [Fe(MgBr)₂] to obtain [Ar- Fe(MgBr)], (II) addition to yield [Ar-(phenyl)-Fe(MgBr)₂], and (III) reductive elimination to return to [Fe(MgBr)₂]. Cycle B did not form [Ar-Fe(MgBr)]. In the first step, phenylmagnesium bromide attacks the intermediate of the oxidative addition directly before [Cl-Mg-Br] dissociates to form [Ar-Fe(MgBr)]. The catalytic Cycle B is favored over the catalytic Cycle Awhen considering the solvent effect. The rate-limiting step in the overall catalytic cycle for both Cycle A and Cycle B is the reductive elimination of [Ar-(phenyl)-Fe(MgBr)₂] to regenerate the catalyst [Fe(MgBr)₂], where the Gibbs free energy in solvent tetrahydrofuran (THF), ΔG_sol, is 82.98 kJ ·mol^-1, as determined using the conductor polarized continuum model (CPCM) method.

Intramolecular hydrogen migration in alkylperoxy reactions is one of the most important reaction classes in hydrocarbon combustion at low temperatures. In this study, the kinetic parameters for reactions in this class were calculated using the isodesmic reaction method. The geometries for all the reactants, transition states, and products were optimized at the B3LYP/6-311+G(d,p) level. A criterion based on conservation of the reaction-center geometry of the transition state was proposed for the reaction class, and the intramolecular hydrogen migration reactions studied were divided into four classes, i.e., (1,3), (1,4), (1,5), and (1,n) (n=6, 7, 8) hydrogen migration. The simplest reaction system for each reaction class was defined as the principal reaction; the approximate single-point energies were obtained at the low level of B3LYP/6-311+G(d,p) and accurate single-point energies were obtained at the high level of CBS-QB3. The other reactions in this class were chosen as the target reactions and the approximate single-point energies were obtained at the B3LYP/6- 311+G(d,p) level. The energy barriers and rate constants of these target reactions were corrected using the isodesmic reaction method. The results showed that accurate energy barriers and rate constants for the reactions of large molecules can be obtained by a relatively low level method using the isodesmic reaction method. In this study, classification of the basic isodesmic reaction showed the essential features of the reaction classes. The present work provides accurate kinetic parameters for modeling intramolecular hydrogen migration reactions of hydrocarbons at low temperatures.

We used first-principles calculations to investigate the photo-induced electron transfer (PIET) process of the hemicyanine-(TiO₂)_n complex ((TiO₂)_n-dye) for n=5, 9, 15. The geometries of the (TiO₂)_n-dye in the ground state were optimized using density functional theory (DFT) and their excited states were investigated using the time-dependent DFT (TDDFT) method. The excited energies, which were calculated using the longrange- corrected functionals, CAM-B3LYP and ωB97X-D, were in good agreement with the experimentally observed values. The wave functions based on DFT were used to calculate the charge transfer integrals by the generalized Mulliken-Hush (GMH) approach. In addition, the photo-induced charge separation rate constant (k_CS) and charge recombination rate constant (k_CR) were calculated using Marcus theory. The calculated results showed that there were a cascade of electron transfer channels from the dye into the (TiO₂)_n cluster, which increases the k_CS value. In contrast, the single channel of charge recombination decreases the k_CR value, which is negligible compared with k_CS, indicating that electron recombination is not favored.

Chlorinated phenols (CPs) are the main precursors for forming the persistent organic pollutants dioxins and have strong teratogenicity, carcinogenicity, and mutagenicity. To explore the novel material for the removal or detection of these pollutants, we used density functional theory calculations to investigate the adsorption behaviors and interaction mechanisms of 2-chlorophenol (2-CP), 2,4,6-trichlorophenol (TCP), and pentachlorophenol (PCP) on pristine and Co-doped (8,0) single-walled boron nitride nanotubes (denoted by BNNT and Co-BNNT, respectively). The results show that compared with BNNT, Co-BNNT introduces local states near the Fermi levels, and has a smaller band gap. BNNT physisorbs 2-CP, TCP, and PCP molecules, whereas Co-BNNT presents chemisorption towards them. Charge-transfer between Co-BNNT and molecules can be clearly observed and the electronic densities of states of the doped systems change significantly near the Fermi levels after adsorption of molecules. Doping with Co atom significantly increases the electronic transport capability of BNNT and enhances the adsorption reactivity of the tube to CPs. Co-BNNT is expected to be a potential material for removing or detecting CPs pollutants.

The adsorption behavior of cinnamaldehyde on icosahedral Au₁₃ and Pt₁₃ clusters was investigated by density functional theory with the Perdew-Burke-Ernzerh of generalized gradient approximation (GGA-PBE). When analyzing the adsorption energies and geometrical parameters of different adsorption models, the adsorption energy of cis-cinnamaldehyde was higher than that of trans-cinnamaldehyde for the same cluster. On the Au₁₃ cluster, the most stable adsorption was the C＝O and C＝C double bond coadsorption model. While on the Pt₁₃ cluster, the most stable adsorption was the C＝O double bond adsorption model. Comparison between the Au₁₃ and Pt₁₃ clusters showed that the adsorption capacity of cinnamaldehyde on the Pt₁₃ cluster was higher than on the Au₁₃ cluster. Analyzing the electronic structures of the most stable adsorption configurations of cinnamaldehyde on the Au₁₃ and Pt₁₃ clusters showed that electrons transferred from 2s and 2p orbitals of cinnamaldehyde to the metal clusters. Electrons of metal clusters were also back-donated to the anti-bonding orbitals of the cinnamaldehyde molecule. This collaborative process eventually led to the stable adsorption of cinnamaldehyde on the Au₁₃ and Pt₁₃ clusters. In addition, adsorption of cinnamaldehyde on cluster models was more energetically favorable than on flat models.

Cyclodextrins (CDs) are widely used in the pharmaceutical industry, and the complex stability constant (logK) is an important evaluation target for CD inclusion complexes. In this work, the structures of the inclusion complexes of 233 compounds with β-cyclodextrin (β-CD) were investigated by the quantitative structure-activity relationship (QSAR) method based on a new set of norm indexes proposed by our group. Here, using several arithmetic approaches, a set of QSAR models based on these new norm indexes were developed to predict the logK values of the β-CD complexes. The results showed that all of the norm indexbased- QSAR models could predict logK well, and the best QSAR model was obtained using the least-squares support vector machine method with correlation coefficient (R), leave-one/ten-out validation correlation coefficient (Q_LOO and Q_LTO) values of 0.9587, 0.8775, and 0.8732, respectively. Comparison with other methods suggested that our method performed better for predicting the logK values of β-CD complexes in terms of both accuracy and stability, especially for the discrimination of isomer structures. The results of this and previous studies demonstrate that it might be possible to use the norm index-based model to predict not only the basic physical-chemical properties, but also the chemical reaction-related constants of organic compounds.

The doping energies and electronic structures of B, N, Si, P, and Co in C₅₀ and C₇₀ were investigated using the density functional theory (DFT)-B3LYP/6-31G^* method, and the structural stabilities of doped fullerenes were investigated based on curvature theory and the electronic structures. The calculated results showed that the doping energies decreased with increasing curvature, and increased with increasing atomic radius of the doping species. Doping with B, N, P, and Co stabilized the C₅₀ structure. However, doping with B and N was disadvantageous for the structural stability of C₇₀. The doping reactivities were mainly determined by the curvature and related to the percentage of nonequivalent carbon atoms in the highest occupied molecular orbital (HOMO), and a large percentage was beneficial for the doping stability. In addition, whether the doped atoms accepted or lost electrons depended on their electronegativity. This work will be helpful for the stabilization of fullerene structures in experiment.

The adsorption and separation behaviors of CO₂ and CH₄ binary mixture in graphene/nanotube hybrid structures (GNHSs) are investigated by grand canonical Monte Carlo (GCMC) combined with molecular dynamics (MD) simulations. CO₂ is preferentially adsorbed in the adsorbents. Compared with a (6, 6) SWCNT (single walled carbon nanotube), GNHSs show improved separation performance. As the temperature rises, the loading of CO₂ reduces rapidly while the loading of CH₄ first increases before being reduced. Finally, the kinetic parameters of CO₂ and CH₄, such as self-diffusivity and residence time, are calculated by MD simulation. The CO₂ molecules diffusing in the GNHS need to overcome a higher barrier relative to that for CH₄. The diffusion of the two components in the adsorption layer outside of adsorbent also influences the separation of the mixture.

The possibility of morphological control of iron oxide as an oxygen carrier for chemical looping combustion was investigated using density functional theory and experiment. First, we calculated the reactivity of Fe₂O₃ with high- index facets [104] and low- index facets [001], as well as the deep reduction reaction mechanism of these two facets. Surface reaction results show that the activity of Fe₂O₃[104] for oxidizing CO is greater than that of Fe₂O₃[001]. Fe₂O₃[104] was reduced into iron oxide at lower oxidation state or into iron, which could then be regenerated after being oxidized by O₂. The deep reduction reaction mechanism between oxygen carrier and CO shows that Fe₂O₃[104] can be completely reduced into Fe, and Fe₂O₃[104] exhibits high oxygen transfer ability. However, Fe₂O₃[001] can only be reduced to a limited extent, with a high energy barrier preventing further reduction, while it also exhibits limited oxygen transfer capacity. Results of experiments further verify the high reactivity and stability of Fe₂O₃[104].

The catalytic decomposition of N₂O using Au₁₉Pd and Au₁₉Pt clusters as catalysts with optimized geometries was studied using density functional theory (DFT). The optimized geometries of the Au₁₉Pd and Au₁₉Pt clusters were obtained as a function of structural and thermodynamic analyses, in which the heteroatoms are on the surfaces of the clusters. We selected the Au₁₉Pd cluster as a model cluster to investigate the reaction mechanism of N₂O decomposition. There are two reaction pathways to be considered: Eley-Rideal (ER) and Langmuir-Hinshelwood (LH). We found that the first N₂O decomposition needs to surmount an energy barrier of 1.118 eV, and is exothermic by 0.371 eV. The elimination of the residual oxygen atom on the surface has an energy barrier of 1.920 eV along the ER pathway after N₂ desorption, which is higher than that along the LH channel (1.669 eV). The adsorption energy of the oxygen atom on the surface is -3.203 eV, and the oxygen atom diffusion on the surface needs to surmount an energy barrier of 0.113 eV along the LH pathway. This indicates that the oxygen atom is prone to transfer on the cluster to promote the generation of the O₂ molecule, and therefore the LH is the optimized reaction pathway. We investigated the catalytic activity of Au₁₉Pt for N₂O decomposition along the LH pathway in comparison with the Au₁₉Pd cluster. Both platinum and palladium have catalytic activities for N₂O decomposition, especially the palladium in this study. Comparison between this work and the theoretical study on periodic systems shows that these two clusters can be used as better catalysts for N₂O decomposition, especially the Au₁₉Pd cluster. Furthermore, the O₂ desorption is no longer the main barrier to the reaction, which further enhances the catalytic activities of these two clusters for N₂O decomposition.

The MP2 and CCSD(T) ab initio quantum chemistry methods were applied to study the pnicogen bonds X―P…S and chalcogen bonds Y―S…P formed between PH2X and SHY (X, Y=H, F, Cl, Br) and the effects of the substituents X and Y on the bonds. Calculated results show that the chalcogen bonds are stronger than the pnicogen bonds. Strongly electronegative substituents that are connected to the Lewis acid strengthened the bonds and significantly affected the structures and properties of the monomers. Conversely, the substituents connected to the Lewis bases produced opposite effects. The energies of chalcogen bonds were 8.37-23.45 kJ·mol^-1; the strongest chalcogen bond was found in the structure HFS-PH₃ using the CCSD (T) method with a bonding energy of 16.04 kJ·mol^-1. The energies of pnicogen bonds were in the range 7.54-14.65 kJ·mol^-1; the strongest pnicogen bond was found in H₂FP-SH₂ using CCSD(T) with a bonding energy 12.52 kJ·mol^-1. The most important factors for bond strength for both types of bonds were the exchange and electrostatic energies. The hyperconjugations lp(S)-σ^*(PX) and lp(P)-σ^*(SY) play important roles in the formation of the pnicogen and chalcogen bonds, which both lead to polarization of the monomers. Polarization caused by the chalcogen bond is larger than that by the pnicogen bond, resulting in the chalcogen bond having less of a covalent character.

Based on first principles and thermodynamics the intrinsic point defect formation energy was calculated at different temperatures and oxygen partial pressures in HfO₂ crystals. The stability of all kinds of point defects as well as the formation of charged point defects and their sensitivity to the Fermi energy was analyzed. We also discuss rules that govern the formation of various point defects that vary with Fermi level. The results show that with a change in temperature and oxygen partial pressure the most stable point defects are obtained (O_i⁰, V_O3²⁺ and Hf_i⁴⁺) when the Fermi level is close to the valence band. The main point defect was the Hf vacancy at a -4 charge when the Fermi level was higher than 3.40 eV. Apart from the Hf vacancy almost no other point defect had an odd charge and they showed negative-U behavior. Using the most stable intrinsic defect as a function of the Fermi level, the oxygen partial pressure and the temperature were determined using three-dimensional defect formation enthalpy diagrams. This diagram provides information that allows for the control of point defects in the crystal.

Density functional theory (DFT) calculations have been used to conduct a detailed study of the mechanism involved the copper(I)-catalyzed hydrocarboxylation of 1-phenyl-propyne using CO₂ and hydrosilane. Theoretical calculations suggested that the activated catalyst Cl₂IPrCuH is initially generated in situ by the reaction of Cl₂IPrCuF with (EtO)₃SiH, and that the entire catalytic reaction involves three steps, including (1) the addition of Cl₂IPrCuH to 1-phenyl-propyne to afford two isomeric copper alkenyl intermediates, which lead to the formation of the corresponding final α,β-unsaturated carboxylic acid derivatives; (2) CO₂ insertion to give the corresponding copper carboxylate intermediate; and (3) σ-bond metathesis of the copper carboxylate intermediate with a hydrosilane to provide the corresponding silyl ester with the regeneration of the active catalyst. The results of our calculations show that the rate-limiting steps for the two paths leading to the two α,β-unsaturated carboxylic acid derivatives are different. In Path a, the alkyne and CO₂ insertion steps were both identified as possible rate-limiting steps, with free energy barriers of 68.6 and 67.8 kJ·mol^-1, respectively. However, in Path b, the alkyne insertion step was identified as the only possible rate-limiting step with an energy barrier of 78.7 kJ·mol^-1. These results were in agreement with the experimental observations. It was also found that the alkyne insertion step controlled the regioselectivity of the products, and that electronic effects were responsible for the experimentally observed regioselectivity.

The second-order nonlinear optical (NLO) properties of bis-cyclometalated iridium(Ⅲ) isocyanide complexes were investigated by density functional theory (DFT). In this work, the geometries of the complexes were optimized using the B3PW91(UB3PW91) functional and they were found to be in good agreement with experimental data. The 6-31G^* basis set was used for the non-metal elements while the LANL2DZ basis set was used for iridium. From the optimized geometries the total first hyperpolarizabilities (β_tot) of the complexes were calculated by the B3PW91(UB3PW91) and B3LYP(UB3LYP) functionals. Because the polarization and diffuse function may have a nontrivial effect on the calculation of the first hyperpolarizabiliy the more flexible and polarized 6-31+G^* non-metal atom basis sets and the LANL2DZ basis set for iridium were used. The absorption spectra of all the complexes were calculated at the CAM-B3LYP(UCAM-B3LYP)/6-31+G^** (LANL2DZ iridium atom) level in acetonitrile to obtain a deeper insight into the second-order NLO properties of these complexes. The results indicate that the second-order NLO response is not strongly affected by different substituents, while the redox reaction plays an important role in improving the second-order NLO response and this comes from a change in the charge transfer pattern and an increase in the degree of charge transfer. The β_tot values of the one-electron oxidized/reduced species (1a²⁺/1a)(complexes cyclometalated with N-arylazolesand alkyl isocyanides, [(C^∧N)₂Ir(CNR)₂]⁺ (R=CH₃)) are 75 and 144 times larger than that of the eigenstate complex (1a⁺), respectively. Therefore, the redox reaction of the cationic bis-cyclometalated iridium isocyanide complexes can effectively tune the second-order NLO properties.

The influence of the substitution of Al for Si on the structural stability and mechanical properties of D8₈-Ti₅Si₃ was determined using first-principles pseudopotential plane-wave methods based on density functional theory. Several parameters including formation enthalpies ((ΔH_f), cohesive energies (ΔE_coh), bulk modulus (B), shear modulus (G),Poisson's ratio (ν), Cauchy's pressure (C₁₂-C₆₆,C₁₃-C₄₄), metallicity (f_m), and Peierls stress (τ_P-N) were calculated. To develop a better understanding of the effects of substitutional Al alloying on the toughness/brittleness of D8₈-Ti₅Si₃ from an electronic structure point of view the density of states, charge density differences and Mulliken population were determined. The results show that the intrinsic brittleness of D8₈-Ti₅Si₃ comes from strong covalent bonding between Ti^6g and Si^6g.When one or two Ti atoms occupy Si sites in the D8₈- Ti₅Si₃ crystal the intensity of covalent bonding between Ti^6g and Si^6g is reduced and the metallicity increases. This is accompanied by the presence of low intensity Al^6g―Si^6g, Ti^6g―Al^6g, and Ti4d―Al^6g bonds. However, when three Ti atoms occupy Si sites in the D8₈-Ti₅Si₃ crystal the Al^6g―Si^6g bonds disappear and the intensity of covalent bonding between Ti^6g and Si^6g increases leading to an increase in brittleness.

The processes involved in the separation of gaseous CH₄/CO₂ mixtures using a nanoporous graphene membrane were simulated using a molecular dynamics method, and the effects of three functional modifications (i.e., N/H, all H, and N/―CH₃ modifications) in the nanopores were analyzed. The results showed that the gas molecules could form an adsorption layer on the surface of the graphene. The adsorption intensity of the CO₂ molecules was higher than that of the CH₄ molecules. The functional modifications in the nanopores not only reduced the permeable area, but also improved the adsorption intensity of the gas molecules by changing the potential distribution of atoms at the edge of nanopores, and therefore affecting the permeability and selectivity of the gas mixture being separated by the nanoporous graphene membranes. Furthermore, the permeability of the CO₂ molecules was as high as 10⁶ GPU (1 GPU=3.35×10^-10 mol·s^-1·m^-2·Pa^-1), which was far greater than those of the existing polymer gas separation membranes. These results therefore demonstrate that nanoporous graphene membranes could be used in an extensive range of applications in industrial gas separation processes, such as natural gas processing and CO₂ capture.

Natural gas is a highly efficient energy source subject to growing demand. Natural gas contains H₂S, which can harmhuman health and cause equipment corrosion and environmental pollution. Effective H₂S adsorbents are necessary to overcome these problems. Grand canonical Monte Carlo (GCMS) simulations were performed to study the selectivity and working capacity (pressure swing adsorption (PSA) and vacuumpressure swing adsorption (VSA) processes) of H₂S in 33 kinds of stable metal-organic frameworks (MOFs), with the aim of separating H₂S from H₂S/CH₄ gas mixture. ZIF-80, Zn₂-bpydtc, CAU-1-(OH)₂, and CH₃O-MOFa were suitable materials for the VSAprocess. CAU-1-(OH)₂ and CH₃O-MOFa were suitable for the PSA process. The structures of materials exhibiting high selectivity and working capacity suggested that appropriate functionality and small pore sizes were important for high selectivity. MOFs with ―Cl, ―OH, and ―OCH₃ functionality exhibited the strongest adsorption. Materials exhibiting high selectivity, strong interaction with H₂S, and large numbers of adsorption sites may have high working capacities. High selectivity and high working capacity stable MOFs were screened and analyzed, to enhance the selectivity and working capacity toward H₂S. This provides a theoretical basis for separating H₂S fromnatural gas using MOFs.

^#271C₅₀Cl₁₀ is widely postulated to be a direct chlorination product of cage ^#271C₅₀. We suggest an alternative formation mechanism of ^#271C₅₀Cl₁₀, based on the topological relationship of these C₅₀ fullerenes. Density functional theory (DFT) calculations of the proposed cage transformation pathway in the chlorination of C₅₀ were performed. The proposed pathway is stimulated by chlorination-promoted fullerene cage transformation, with a lowactivation barrier. DFTcalculations of the Stone-Wales (SW) transformation pathways revealed that the thermodynamically favored rearrangement of other C₅₀ chlorofullerene into ^#271C₅₀Cl₁₀ requires a lower activation energy than that of the pristine carbon cage. This suggested that it is a more effective pathway of chlorinating C₅₀ to ^#271C₅₀Cl₁₀.

Themethylation of 4-methylbiphenyl (4-MBP) can yield 4,4'-dimethylbiphenyl (4,4'-DMBP), an important precursor for advanced polymers. The reaction mechanismof the shape-selective methylation of 4-MBP with methanol within the pores of H-ZSM-5 zeolite was studied, using“our own-N-layered integrated molecular orbital+molecular mechanics”(ONIOM) and density functional theory (DFT) methods. Stepwise and concerted mechanisms were considered, with the former having a lower activation energy. 4,4'-DMBPis kinetically favored by both mechanisms. Transition state selectivity accounts for the preferential methylation to 4,4'-DMBP. The isomerization of 4-MBPto 3-methylbiphenyl (3-MBP) is restricted within the zeolite. The isomerization of 4-MBP to 3-MBPis kinetically favored over methylation on the external zeolite surface, which causes a decrease in 4, 4'-DMBP selectivity. Passivating the external surface will suppress 4-MBP isomerization, therefore increasing 4,4'-DMBP selectivity by restricting reaction within the zeolite. The computational results of shape-selective and non-selective reactions over H-ZSM-5 zeolite well account for the experimental observations.

Time-dependent density functional theory has been used to investigate the plasmon excitation processes in silicene quantumdots. Two main plasmon resonance bands were observed running parallel to the direction to the silicene quantumdot plane around 2.0 and 7.0 eV. Given that delocalized π electrons can participate in the excitation of the two plasmon resonance bands, an increase in the side length of the rectangular silicene quantumdots in the direction of the excitation led to the red-shifting of the two main plasmon resonance bands. Plasmon excitation in silicene quantumdots is also dependent on the edge configuration. Furthermore, because of the relatively high symmetry of the hexagonal silicene quantum dot, the plasmon resonance modes of the quantumdots were found to be identical along the different excitation directions running parallel to the quantumdot plane.

Quantitative structure-property relationship (QSPR) studies on retention and separation factors of chiral compounds play a key role in predicting the retention and separation factors even the elution order of enantiomers. Chiral diarylmethane derivates were selected for computing molecular structural descriptors using VolSurf program. Models were built between the descriptors and retention as well as separation factors. The robustness of the model with respect to separation factors was assessed by external validation through the test set, leave-many-out cross-validation and Y-randomization test. The results were satisfactory. Analysis on the variables shows that the molecular globularity, hydrophilic regions at median energy levels, hydrophilic-lipophilic balance, amphiphilic moment, suitable hydrogen bond donors and acceptors are beneficial to the retention of enantiomers on the chiral stationary phase. Large differences of the hydrophilic regions at high energy levels, hydrophobic regions at lowenergy levels, amphiphilic moment, suitable hydrogen bond donors and acceptors, and anion regions between enantiomers are advantageous to the separation of enantiomers on the chiral stationary phase. These models allowthe prediction of retention and separation factors, especially the elution order of enantiomers.

Molecular dynamics (MD) simulations have been carried out to study the micro-interfaces between counterions (Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺) and dodecyl sulfate surfactant at the air/liquid interface. The morphology of the monolayer was analyzed by the density profile of the surfactant components, and the interactions between the polar head groups of the surfactants and the counterions were analyzed using the radial distribution function (RDF). The results showed that the interfacial thickness and thicknesses of the Stern and diffusion layers increased as the radius of counterion increased, whereas the surface tension and the degree of counterion association at the adsorbed layer decreased as the radius increased. These results indicated that the different counterions had a significant effect on the adsorption behavior of the dodecyl sulfate surfactants at the interface.

The configuration, stability, and electronic structure of W₃O₉ clusters deposited on Li- and Al-doped MgO(001) surfaces were investigated using first- principles molecular dynamic simulations combined with quantum mechanical calculations. The results indicated that when the doping was in the top layer of the MgO (001) surface, the type of dopant had a great influence on the configuration of theW₃O₉ clusters. In the presence of electron-deficient Li doping, the cyclic conformation of the gas-phase W₃O₉ clusters was not stable, and it changed to a chain-like structure. While the introduction of the Al dopant made the surface electron-rich, the W₃O₉ clusters preferred parallel and vertical arrangements, respectively; the stabilities of the two configurations were similar, except that in the former case the one terminal oxygen of the clusters became a capped oxygen via bonding with three W atoms. When the doping was present in the sublayer, the W₃O₉ clusters still showed a cyclic conformation, and favored a vertical deposition model. In comparison with the Li-doping of the MgO(001) surface, the Al-doping significantly enhanced the interactions between theW₃O₉ and the MgO(001) surface, and more electrons were transferred from the substrate to certain W atoms, which would have significant effects on the catalytic performance of the W₃O₉ clusters.

Au/H similarity is a hot topic in chemistry. Here, we report the theoretical prediction of new members of the Au/H analogy family: covalent B₂Au₄, ionic Al₂Au₄, and BAlAu₄. A comparative study of the geometric and electronic structures of electron-deficient B₂Au₄, Al₂Au₄, and BAlAu₄ was performed based on density and wave functional theories. Detailed orbital analyses, adaptive natural density partitioning (AdNDP), and electron localization function (ELF) analyses were performed. Ab initio theoretical evidence strongly suggests that the ground state of slightly distorted C₂B₂Au₄ is a covalent complex containing two B―Au―B three centers-two electrons (3c-2e) bonds. Unexpectedly, C_3vAl⁺(AlAu₄)^- and C_3v Al⁺(BAu₄)^- are predicted to have a salt-like composition with three X―Au―Al 3c-2e bonds (X=Al in Al₂Au₄, X=B in BAlAu₄). Al₂Au₄ and BAlAu₄ represent the first examples of bridging gold bonds in ionic-deficient systems. The adiabatic and vertical detachment energies of the anions were calculated to facilitate their future experimental characterization. Bridging gold addressed in this work provides an interesting bonding mode for covalent and ionic-deficient systems, and may aid in designing new materials and catalysts with highly dispersed Au atoms.

The compatibilizing effects of the addition of a block copolymer on the mechanical properties of immiscible polymer blends were studied using a combined simulation method; this method used MesoDyn to determine the morphology and a probabilistic lattice spring model (LSM) to determine the mechanical properties. The mechanical properties, including the Young's modulus, tensile strength, and fracture position, were analyzed as a function of the concentration of the additive. The simulation results showed that the polymer blends without any compatibilizer had poor mechanical properties, compared with the original components, primarily because of the lack of stress transfer across the sharp interface. The tensile strength increased dramatically with the addition of the compatibilizer. The fracture position moved from the interface further into the matrix with increases in the volume fraction of the compatibilizer, leading to the enhancement of the tensile strength. The Young's modulus varied slightly with increases in the concentration of the additive. These studies provide an efficient path for the correlation of the complex morphologies of polymer blends with their mechanical response.

The adsorption of thiophene on Pd(111), Pt(111), and Au(111) surfaces was investigated by periodic density functional theory (DFT) calculations at the GGA/PW91 level. The results showed that the adsorption energies of thiophene on the different surfaces following the order Pd(111)>Pt(111)>Au(111). The adsorption structure on the Au(111) surface showed almost no change, and the most stable adsorption structure was tilted adsorption on the top site through the S atom of thiophene. For the Pd(111) and Pt(111) surfaces, the most stable adsorption structure was parallel adsorption to the hollow site through the ring plane of thiophene. After adsorption, the H atom of thiophene moved upward and the structure of thiophene was distorted and folded. The aromaticity of thiophene was disrupted and the C atoms were characteristic of sp³ hybridization. Furthermore, the electrons of the M(111) surfaces and thiophene were redistributed after adsorption. The electron transfer from thiophene to the M(111) surfaces was in the order Pd(111)>Pt(111)>Au(111). The electrons of the M(111) surfaces were also back-denoted to the empty orbitals of the thiophene molecule. These processes eventually lead to the adsorption of thiophene on the M(111) surfaces.

Raman spectroscopy combined with density functional theory (DFT) calculations provides information at the molecular level to understand weak intermolecular interactions relevant to molecular structures. In this work, the influence of the fundamental properties of thiourea on the Raman spectra of thioureawater complexes was investigated using DFT calculations. The results showed that hydrogen bond interactions can change the order of the frontier orbitals and directly influence the Raman spectra of thiourea. In addition, the keto-enol tautomerization of thiourea cannot occur in neutral aqueous solution because of the large positive Gibbs free energy change.

Grand canonical ensemble Monte Carlo (GCMC) simulations were performed to investigate the purification of benzene from air by single-walled carbon nanotubes (SWNTs). It was found that (20,20) SWNT with a large diameter is suitable to adsorb pure benzene. For the removal of benzene in air, the minimum and maximum selectivities were observed for the (12,12) SWNT at 4.0 MPa and the (18,18) SWNT at 0.1 MPa, respectively. To obtain deep insight into the unusual behavior, we analyzed the local density profiles, snapshots, and probability profiles of N₂-O₂-C₆H₆ mixtures. The results showed that the (18,18) SWNT was entirely occupied by benzene molecules, while, for the (12,12) SWNT, N₂ andwere prone to appear in the interstices between tubes, instead of inside tubes, because of stronger adsorbate-adsorbent interactions. Additionally, we calculated the orientation order parameters of the adsorbates. The results suggested that benzene molecules prefer lying nearly flat on the pore surface, while N₂ and O₂ molecules orient parallel to the pore axis. Finally, the effects of temperature and concentration on the selectivity of benzene were investigated. We found that with increasing temperature the selectivity in large pores decreased more evidently than that in small pores. By contrast, the concentration plays a more important role in affecting the selectivity in small pores.

To control the kinetic oscillations for the purpose of obtaining a high conversion rate, external forcing of methane oxidation on metal catalysts was studied with kinetic Monte Carlo simulations. The influence of composition cycling of the feed on the dynamics and conversion rate was investigated. The results showed that the composition cycling of feed cannot give rise to different kinetic behavior, such as short periods or doublepeaks, but does bring about a higher conversion rate. It was shown that with forcing periods from T/3 to 2T (T is the average period of autonomous oscillations), the oscillations changed from short periods and small amplitudes to typical double-peak oscillations. The conversion rate can also be calculated, and the results showed that the mean conversion was slightly higher with forced oscillations. The changing of the kinetics can be attributed to phase transition of the metal catalysts from the oxidized surface to a partially reduced state.

The deformation mechanisms and mechanical tensile behavior of Ag nanowires containing different densities of parallel twin boundaries were investigated using molecular dynamics simulations. The effect of twin boundaries on the Young's modulus in nanowires was not obvious in the elastic deformation stage. After the elastic deformation stage, the initial dislocation from the edge of the free surfaces in nanowires resulted in plastic deformation. The existence of the twin boundary in nanowires will cause the spread of the dislocation and act as sources of dislocations with the assistance of the newly formed defects with further tension load. The simulation showed that the mechanical strength of Ag nanowires was highly dependent on the twin boundary spacing and the size of the grain, resulting from the aspect ratio between the spacing distance and the length of the cross-section. In particular, twinned Ag nanowires with small twin density (aspect ratio > 1) had small yielding stresses, even less than that of the single crystal Ag nanowires. Only with large twin density (aspect ratio < 1) can the nanowires be strengthened by the structure of the twin boundaries. We also investigated the effects of tensile rate and temperature on the yielding strength of the Ag nanowires. With increasing temperature, the difference of yielding stress between twinned nanowires and single crystal nanowires first increased and then decreased to a stable level. With increasing tensile rate, this difference showed the opposite trend.

From the viewpoint of the elastic-plastic microscopic mechanisms of explosives, we investigated the microscopic physical and chemical responses of seven dominant slip systems in the β-octahydro-1,3,5,7- tetranitro-1,3,5,7-tetrazocine (β-HMX) single crystal under low pressure and long pulse loading using the ReaxFFforce- field-based molecular dynamics method. The simulation results suggest that the seven slip systems exhibit different physical and chemical responses for loading orientations normal to the (001), (101), (100), (011), (111), (110), and (010) crystal planes. The shear stress, energy, temperature, and chemical reaction strongly depend on the loading direction. For the (010) plane, the shear stress barrier is very high, which leads to fast energy accumulation and temperature increment that contribute to the early bond-breaking process, making it the most sensitive direction. For the (001) plane, the small shear stress barrier results in slow energy accumulation and temperature increase, and thus little bond dissociation, making it the least sensitive direction. The reaction sensitivity of the slip system is suggested to be significantly related to the intermolecular contacts on the two sides of the slip plane (i.e., steric hindrance) and the reaction activity of contacted atoms or groups. Directions with large steric hindrance and high reaction activity lead to high reaction sensitivity, whereas directions with small steric hindrance or low reaction activity result in low reaction sensitivity. The slip system with relatively high chemical reaction sensitivity is suggested to be associated with the origin of“hot spots”in energetic single crystals. This study provides theoretical support for developing a more reasonable and reliable sensitivity evaluation method for high explosives.

A multiscale simulation strategy was designed based on the features of polyurethane. With this strategy, we investigated the mechanical properties and glass transition temperatures of polyurethane materials crosslinked by different reactants or with different functionalities of the same reactants. From the atomistic simulation results, a coarse-grained dissipative particle dynamics model combined with the reaction module was constructed. Then, this simulation was used to describe the diffusion of components as well as the crosslinking process and the formation of the network structure. Finally, the reverse-mapping scheme was used for atomistic representation and to analyze the mechanical properties and glass transition temperature of the system. This multiscale simulation strategy can be expanded to other complex systems with competing dynamic influencing factors.

Several new porous aromatic frameworks (PAFs) were designed by Li doping or B substitution based on the PAF-301 molecular model. The hydrogen storage capacities of these materials were investigated using quantum mechanics and molecular mechanics methods. First, the binding energies between H₂ and the different molecular fragments were calculated using quantum mechanics, and the atomic charge distributions of the molecular fragments were calculated by the density-derived electrostatic and chemical charge (DDEC) method. Then, the adsorption equilibrium properties of H₂ on the different PAFs were calculated at 77 and 298 K using grand canonical Monte Carlo (GCMC) simulations. The results indicate that the binding energy between H₂ and benzene without Li doping is poor, while the binding energies between H₂ and Li-doped six-member rings are improved. Li atoms doped into the benzene ring result in higher positive charges, and the electronegativity of the original carbon atoms in the benzene ring increase after its two carbon atoms are replaced with two boron atoms. Among these new materials, PAF-301Li has the highest hydrogen storage capacity at 77 K, while PAF-C₄B₂H₄-Li₂-Si and PAF-C₄B₂H₄-Li₂-Ge have better hydrogen storage capacities at room temperature than at 77 K. However, the hydrogen storage capacities of these various materials at room temperature are far below the capacities at cryogenic temperature. The preferential adsorption sites for H₂ on the PAFs at 77 K were analyzed through the potential energy surfaces and mass center density distribution of the adsorption equilibrium. It was found that there are four obvious high-density adsorption regions in the frameworks of PAF-301 and PAF-301Li because of their wide low-energy regions in the crystal center, while there are only two distinct high-density adsorption regions in the other three PAFs because of their narrow low-energy regions in the unit cell center.

To accurately predict the capability and possible reaction site for atoms in molecules to donate or accept electrons in chemical processes, i.e., to quantitatively determine electrophilicity, nucleophilicity, and regioselectivity, is an important yet incomplete task. Earlier, we proposed using the Hirshfeld charge and information gain as two equivalent descriptors for this purpose, based on the Information Conservation Principle we recently proposed. This idea was successfully applied to two series of molecular systems to confirm its validity. However, our previous work is hindered by the fact that the involved element is carbon. It is unclear if stockit applies to other elements and to different valence states of the same element. In this study, to address these issues, the method was applied to nitrogen-containing systems. Five different categories of compounds were studied, including benzenediazonium, azodicarboxylate, diazo, and primary and secondary amines, with a total of 40 molecules. The results show that there are strong linear correlations between the Hirshfeld charge and their experimental scales of electrophilicity and nucleophilicity. However, these correlations depend on the valence state and bonding environment of the nitrogen element. The linear relationship only holds within the same category. Possible reasons for this observation are discussed.

The hydrodesulfurization (HDS) of thiophene on an γ-Mo₂N(100) surface was investigated by density functional theory (DFT) and different configurations of thiophene on γ-Mo₂N(100) surface were considered. After geometric optimization, it was confirmed that the η5-Mo₂N configuration was the most stable adsorption model with an adsorption energy of -0.56 eV, where thiophene absorbed on 4-fold hcp vacant sites parallel to the surface with the S atom bonded to a Mo2 atom. The stable coadsorption of H atoms and thiophene on hcp sites showed that the hcp site is the active site for thiophene HDS on γ-Mo₂N(100). A direct desulfurization reaction pathway in HDS of thiophene dominated the process on the γ-Mo₂N(100) surface, which could be divided into the removal of the S atom and the hydrogenation saturation of C₄ species. To identify the intermediate products and the most probable reaction mechanism of thiophene HDS, a transition state search was carried out. The results indicated that the reaction of the first H atom required an activation energy of 1.69 eV, which was the rate-determining step in the HDS of thiophene. The thiol group (―SH) and butadiene were preferentially formed after hydrogenation of thiophene, and ―SH detached from mercaptan was the intermediate of H₂S. 2-Butene and butane were the products of the hydrogenation saturation of butadiene. H₂S, 2-butene, and butane were easily desorbed from γ-Mo₂N(100) to give the products because of weak adsorption.

Uranyl ion adsorption on the hydroxylated α- quartz (101) surface was investigated by firstprinciples density functional theory calculations. We explicitly considered the first hydration shell of the uranyl ion for short-range solvent effects and used the conductor-like screening model (COSMO) for longrange solvent effects. Both the adsorption energies and electronic structures of the adsorption system indicated that the bidentate hydrated uranyl species were more stable than bidentate hydroxylated species, and bidentate adsorption of the uranyl ion on the bridge site of dia-O_s1O_s2 was the most stable adsorption model in the aqueous state. The large differences in the electronic structures of the two forms were mainly because of the different degree of bonding between uranium and the surface after adsorption, which makes the 5f orbital narrow and causes a red shift. Use of halogen ions in the uranyl coordination environment can adjust the band gap of the uranyl adsorption system.

The TiC monolayer sheet, a new two-dimensional structure, is proposed as a promising hydrogen storage material because of its high specific surface area and the large number of exposed Ti ions on the surface. First principles calculations showed that both chemisorption and physisorption of H₂ can take place on the TiC sheet surface, with adsorption energies of 0.36 and 0.09 eV per H₂, respectively. For 1 and 1/4 monolayer (ML) coverages, the dissociation barriers of H₂ on the TiC sheet surface were calculated to be 1.12 and 0.33 eV, respectively. Thus, as well as physisorption and chemisorption, there were dissociated H atoms on the TiC sheet surface. The maximum H₂ storage capacity was calculated to be up to 7.69% (mass fraction). The capacities were 1.54%, 3.07%, and 3.07% for dissociated H atoms, and chemisorption and physisorption of H₂, respectively. Considering only Kubas adsorption, the hydrogen storage capacity was 3.07%. The adsorption energy for H₂ chemisorption on the TiC sheet surface only slightly changed at different coverages, which benefits the storage and release of H₂.

Much attention has been given to the optical properties of noble metal nanostructures and these are closely related to the size, morphology, and environment of the nanoparticles. In this paper, the influences of structures and assembly modes on the surface plasmon resonance (SPR) of Au nanorods were studied through a finite-difference time-domain (FDTD) simulation on Au nanorod assemblies (dimers and multimers) of different configurations. The simulated optical spectra agree well with the experimental results. The simulated results for the side-by-side (S-S) oriented Au nanorods indicate that the transverse SPR (SPR_T) has a slight redshift, and the longitudinal SPR (SPR_L) blue-shifts obviously. For the end-to-end (E-E) oriented Au nanorod dimer, the results indicate that with a decrease in the gap spacing of the E-E oriented Au nanorods, the SPR_T does not shift while the SPR_L red-shifts obviously. Moreover, a new coupling SPR peak appears in the near-infrared (NIR) region, blue-shifting and enhancing with a decrease in the gap spacing. Based on the spring oscillator model and the polarization of the nanoparticles under an incident electric field, we propose a reason for the SPR shift and the appearance of a new coupling SPR for the Au nanorod assemblies.

It is investigated that the minimum-energy structures and energetics of clusters of the larger linear HCCCN molecule with small numbers of para- hydrogen molecules with pairwise additive potentials. We performed the optimization of the minimum-energy structures using a genetic algorithm. It was found that p-H₂ molecules filled three solvation rings around the HCCCN axis, each of which contained up to six p-H₂ molecules, followed by accumulation of two p-H₂ molecules around the hydrogen and nitrogen ends of the HCCCN molecule. The first solvation shell was completed with number of p-H₂ molecules (N)=20. The chemical potential was calculated, and the N dependence of the chemical potential μ(N) showed oscillatory behavior.

The electronic structure tailoring of GaAs nanowires through surface modification was investigated by first-principles calculations. The effect of different surface-passivation materials (H, F, Cl, Br, and I) on the electronic structure of the GaAs nanowires was studied. The results show that for different atoms, the tailoring of the electronic structure is mainly determined by their passivation ability. The surface modification tunes the bandgap and also the bandgap types. The electronic structure of the GaAs nanowires was determined by the surface states and the quantum-confinement effect jointly. The amplitude of the bandgap variation on the diameter is different for the GaAs nanowires modified with different materials. Surface modification offers a new way to tailor the bandgap of GaAs nanowires without changing their diameter or crystal structure.

The formation energy of different ensembles on Pd(111) surfaces containing N (N=1-4) Au atoms were investigated using a density functional theory model. The best model for exploring the adsorption of thiophene was selected, and the mechanism of competitive hydrodesulfurization on a Au/Pd(111) bimetallic surface was investigated. The results showed that Au/Pd(111) has the lowest formation energy, and adsorption at the hexagonal close-packed site is most stable when the thiophene plane is tilted at 30° to the Au/Pd(111) bimetallic surface with S atom. The reactions are exothermic, and desulfurization can be either direct or indirect. The direct desulfurization pathway has a low activation energy, but it is difficult to control the products. The indirect desulfurization pathway is the best fit for the cis-hydrogenation process; C―S cleavage has the highest reaction energy barrier, and is the rate-determining step. The activation energy barrier of the rate-determining step on Au/Pd(111) is lower than those on Au(111) and Pd(111). This indicates that bimetallic AuPd is more active than single Au and Pd in the hydrodesulfurization of thiophene.

Ab initio calculations have been performed for a group of 59 aromatic compounds at the HF/6-31G^* level of theory. Electrostatic potentials (ESPs) and the statistically based structural descriptors derived from ESPs on the molecular surface have been obtained. The linear relationships between the adsorption equilibrium constants of organic contaminants by carbon nanotubes and the theoretical descriptors have been established by multiple linear regression. It is shown that the quantities derived from electrostatic potentials, V_min, σ₊² and ΣV_ind⁺ together with the molecular surface area (S) and the energy level of lowest occupied molecular orbital (ε_LUMO) can be used to express the quantitative structure-property relationship (QSPR) of this sample set. All of the descriptors introduced in the QSPR models have definite physical meanings and their reasonability can be explained in terms of intermolecular interactions between the aromatic pollutants and carbon nanotubes or water. The stabilities and predictive powers of the models have been validated by "leave-one-out" and Monte Carlo cross-validation methods. Three nonlinear modeling techniques, namely supported vector machine (SVM), least-square supported vector machine (LSSVM), as well as Gaussian process (GP), have also been used to construct the predictive models. Though the SVM and LSSVM models exhibit strong fitting abilities, their predictive powers are inferior to the other models tested. The GP model yields the best fit and predictive ability among all of the models. Its advantage over the linear model, however, is not as remarkable as expected, which means that the relationship between the molecular structure and the adsorption property for the present system is primarily linear.

Molecular dynamics simulations of a methanol-water mixture (molar ratio 1:1) were performed to determine the differences among the structural and transport properties in three carbon nanotube (CNT) systems: an equilibrium system, a system with an external pressure, and a system with a gradient electric field. The simulations showed that in both the equilibrium system and the system with an external pressure, the methanol-water mixture is clearly immiscible in the CNTs, with the water molecules distributed mainly around the tube axis, and the methanol molecules located near the tube wall; however, in the system with a gradient electric field, the hydrophobic CNTs become hydrophilic, and the phenomenon of methanol-water separation disappears. In contrast, unlike the unidirectional transport observed in the system with an external pressure, the particles move in two directions in the system with a gradient electric field, with a flow one order of magnitude larger than that in the corresponding external pressure system. However, in the system with a gradient electric field, the net flux is small, because the flows for the two directions are similar. There is thus a small flux difference between the system with an external pressure and the system with a gradient electric field.

Recent experimental results have indicated that the negative thermal expansion is a common phenomenon in PbTiO₃-based materials, and that this expansion is affected by various substitutions. Interestingly, Cd substitution in PbTiO₃ has a unique effect compared with other A-site substitutions, in that it enhances negative thermal expansion. Therefore, studying A-site substitution in PbTiO₃, the role of which still remains unclear, would provide a deeper understanding of the nature of the negative thermal expansion of PbTiO₃-based materials. Herein we report the results of structural calculations, densities of states and the minimumelectron densities of Pb_1-xSr_xTiO₃, Pb_1-xBa_xTiO₃, and Pb_1-xCd_xTiO₃ supercells on the basis of chemical bond first-principles calculations. The results demonstrate that the hybridization between Cd―O orbitals is more pronounced than that between Pb―O orbitals, while the bonding between Ba/Sr and O is almost ionic in nature. Cd substitution was found to have an unusual effect in terms of enhancing the average bulk coefficient of thermal expansion in PbTiO₃. In contrast, Ba and Sr substitutions reduce the coefficient. Thus, the covalency in the bonding between the A- site and O in PbTiO₃- based materials is responsible for the enhanced negative thermal expansion.

The gas composition in natural gas hydrate deposits is complex, and therefore the use of spectroscopic analysis to elucidate the chemical composition is of great significance. Using density functional theory (DFT) calculations at the B97-D/6-311++G(2d, 2p) level, we systematically explored the stability of 18 alkane guest molecules in two standard water cavities (5¹²6² and 5¹²6⁴). The results indicated that most alkane guest molecules can be stored in the 5¹²6² cage, with the exception of 3-methylpentane and 2,3-dimethylbutane, while all 18 alkanes can be encapsulated in the 5¹²6⁴ cage. The Raman spectroscopic characteristics of five straight-chain and four cyclic alkane guest molecules in the 5¹²6² and 5¹²6⁴ cages were also simulated. The majority of the Raman bands of the straight-chain alkanes in the C―H stretching region were found to move to higher wavenumbers as the number of carbon atoms increased, while most bands of the cyclic molecules in this region transitioned to lower wavenumbers. These theoretical results should prove helpful with regard to identifying hydrate deposits from experimental Raman spectroscopic data.

Multireference approaches have commonly been employed to calculate low-lying states of openshell molecules with spin-orbit coupling (SOC), such as for AuO and AuS. However, by choosing a proper reference state, the equation-of-motion coupled-cluster approach (EOM-CC) can also be used to calculate some low-lying states of these molecules. Furthermore, the EOM-CC approach is a single-reference method and, therefore, more easily employed than multireference approaches. In this work, low-lying states of AuO and AuS are investigated based on a recently developed EOM-CC approach for ionization potentials (EOMIP-CC) with SOC at the CCSD level, using the corresponding anions as reference. The contribution of triples with EOMIPCC is estimated by comparing results of EOMIP-CCSD and EOMIP-CCSDT at a scalar relativistic level. In addition, compared with the EOMIP-CCSDT results, errors by UCCSD(T) can reach 0.1-0.15 eV when spin contamination is significant and the norm of T₁ is sizeable. When SOC is present, bond lengths and harmonic frequencies obtained with EOMIP-CCSD for the investigated states are in reasonable agreement with experimental data. Furthermore, ionization energies corresponding to the high-lying ²Δ_3/2, ²Σ_1/2⁺, and ²Π_1/2 states are overestimated by EOMIP-SOC-CCSD, but results for the other low- lying states agree well with the experimental data, with an error of approximately 0.2 eV. These results indicate that the single-reference EOMIPCCSD method with SOC is able to provide a reasonable description of low-lying states of AuO and AuS.

The adsorption behavior and selective hydrogenation reaction mechanisms (C=O addition, C=C addition, and 1,4-conjugate addition) of cinnamaldehyde on an Au(111) surface were investigated by density functional theory combined with a periodic slab model. The adsorption energies of various adsorption models were obtained to determine the preferred adsorption configuration. The calculated results indicate that the most stable adsorption configuration involved the C=O and C=C double bond adsorbed on the Au(111) surface, with an average adsorption energy of 140.0 kJ·mol^-1. The transition states of each elementary reaction for all possible reaction mechanisms were also located. Comparison of the activation energy barriers revealed hydrocinnamaldehyde (HCAL) to be the most likely selective hydrogenation product of cinnamaldehyde on an Au(111) surface. In addition, the 1,4- conjugate addition mechanism, which generates 3-phenyl-1-propen-1-ol (ENOL) that readily tautomerizes to HCAL, required less activation energy than did the C=C direct addition mechanism. The dominant reaction pathway involved an O atom of cinnamaldehyde preferentially hydrogenating to generate a more stable allyl intermediate. Another H atom then added to a C atom directly connected to the phenyl ring of the allyl intermediate to yield ENOL. Finally, ENOL tautomerized to HCAL. Throughout the process, the generation of ENOL is the rate-determining step, for which the highest activation energy barrier was required.

Using density functional theory with the B3LYP functional, the optimized geometrical structures of the M@t-Bu-calix[4]arene and (M@t-Bu-calix[4]arene)Li' (M=Li, Na, K) compounds were obtained. Five stable isomers were identified for each bi-alkali-metal-doped (M@t-Bu-calix[4]arene)Li' species. The first three lowlying isomers have considerable intramolecular interaction energies between alkali metal atoms and the t-Bucalix[4]arene molecule, indicating their stabilities. According to natural bond orbital analyses, the outside Li' atom is negatively charged in some (M@t-Bu-calix[4]arene)Li' structures, indicating the alkalide characteristics of these isomers. In addition, the nonlinear optical (NLO) properties of isolated and alkali-metal-doped t-Bu-calix [4]arene molecules were calculated using the CAM-B3LYP method. The results indicate that the single-doped effect of alkali metalMgreatly enhances the first hyperpolarizability (β₀) of the t-Bu-calix[4]arene molecule. In particular, when another Li atomis doped outside the M@t-Bu-calix[4]arene species, the resulting (M@t-Bucalix[4]arene)Li' compounds exhibit larger β₀ values. Obviously, the alkali-metal-doping effect plays a crucial role. The MLi'-4 conformation has the largest β₀ value (41827-114354 a.u.) among all the (M@t-Bu-calix[4]arene) Li' structural isomers, and it is found that the β₀ value of (M@t-Bu-calix[4]arene)Li' gradually increases with increasing atomic number of the alkali metal M. Therefore, alkali-metal doping is an effective approach to enhance the NLOresponse of the t-Bu-calix[4]arene molecule.

The adsorption of Au, Ag and Cu atoms on either one side or both sides of defected graphene were studied based on first-principles, using density functional theory (DFT), and the adsorption energies as well as the magnetic, charge transfer and electronic structures of the systems were calculated and analyzed. Compared with perfect graphene, the adsorption energies of Au, Ag, and Cu atoms on defected graphene were found to increase by more than 2 eV, demonstrating that the metal atoms are more easily absorbed at defect locations. Analysis of the electronic structures and charge density differences of these adsorption systems showed that chemisorption takes place between the Au, Ag, and Cu atoms and vacancy defects. The magnetic property results indicated that each of these three adsorption systems are magnetic. In the case of single-sided adsorption, the magnetic moments are approximately 1μ_B, while for double-sided adsorption, the magnetic moments are about 2μ_B.

Although trehalose is used as a protein stabilizer, the mechanism by which this stability is induced is not fully understood at present. In this study, we investigated the interactions between trehalose and all 20 common amino acids using all-atom molecular dynamics simulations. It is found that all the amino acids exhibit a preference for contact with water, especially the polar and charged amino acids. Conversely, only the hydrophobic amino acids were found to have a slight preference for contact with trehalose molecules. This tendency is most pronounced in the case of contact between trehalose and aromatic or hydrophobic side chains, whereas the backbones of each amino acids all show similar propensities for contact with water. Furthermore, hydrogen bonds between amino acids and trehalose were found to be significantly weaker than those between amino acids and water, although both trehalose and water can interact with the amino acids via hydrogen bonds. These findings are important with regard to the exploration of the molecular mechanism of protein stability induced by trehalose and the rational design of highly efficient protein stabilizers.

The geometric and electronic structures, energetics, and vibrational frequencies of different coordinate systems formed between 15 conformers of proline (Pro) and Cu, Cu⁺, and Cu²⁺ were investigated in detail, using the M06-2X and ωB97XDmethods with 6-311++G(2d, p) and TZVPbasis sets.Atotal of 20, 16, and 16 stable [Pro-Cu]^0/1+/2+ complexes were obtained at four levels. These structures demonstrated that 12 conformers of Pro exist in the [Pro-Cu] and [Pro-Cu]⁺ systems, while 11 conformers are present in the [Pro-Cu]²⁺ complexes. The most stable complexes are evidently not formed by the lowest energy conformer of Pro with Cu, Cu⁺, and Cu²⁺. In the CI3, CI4, CII7, and CII8 complexes, the carboxyl group hydrogen of Pro was found to transfer to the imino nitrogen to forma zwitterion. Both the relative energy difference and the deformation energy of Pro gradually increase along with the charge number of the Cu. The binding energies of the [Pro-Cu]^0/1+/2+ systems were determined to be in the ranges of -60.0 to -5.0, -340.0 to -170.0, and -1100.0 to -860.0 kJ· mol^-1, respectively. The stretching vibrational frequencies of the N―H and O―H bonds in Pro all exhibit a general red shift on complexation. Additionally, each systemshows charge transfer fromthe Pro to the Cu, even in the case of [Pro-Cu]²⁺, some complexes that have more than one negative charge.

Near-infrared plasmons in N-doped hexagonal graphene nanostructures were investigated using time-dependent density functional theory. Along a certain direction, N-doped hexagonal graphene nanostructures with a side length of 1 nm have more intense plasmon resonances throughout the nearinfrared spectral region. The electrons that participate in these near-infrared plasmon resonances oscillate back and forth between the center and edge regions of the hexagonal nanostructures. The formation of a near-infrared plasmon resonance mode depends on the nitrogen-doping position and the scale size of the graphene nanostructure. It is only when the nitrogen-doped location is close to the edge of the nanostructures, near-infrared plasmon resonance mode of the graphene nanostructure will be formed. For N-doped hexagonal graphene nanostructures with a side length of less than 1 nm, there is no plasmon resonance in the nearinfrared spectral region.

Using the classical Monte Carlo method and density functional theory (DFT) calculations, various stable adsorption configurations for the Ni/yttria-stabilized zirconia anode (Ni/YSZ) were predicted. Compared with previously reported results, more stable triple phase boundary structures were found. Based on these optimized configurations, charge transfer is discussed in detail, as O ion migration occurs where electron transfer from YSZ to Ni is important in describing the electrochemical reaction at the anodes of the solid oxide fuel cells. We thus analyzed the possible factors that affect the degree of electron transfer. The results indicate that a new electrochemical mechanism is at work in the Ni/YSZ system.

The reaction mechanism and rate constant of the H₂O₂+Cl reaction, with and without a single water molecule, was investigated theoretically at the CCSD(T)/aug-cc-pVTZ//B3LYP/aug-cc-pVTZ level of theory. The calculated results show that there is only one channel for the formation of HO₂+HCl in the naked H₂O₂+Cl reaction with an apparent activation energy of 10.21 kJ·mol^-1. When one water molecule is added, the product of the reaction does not change, but the potential energy surface of the reaction becomes complex, yielding three different channels RW1, RW2, and RW3. The single water molecule in the RW1 and RW2 reaction channels has a negative influence on reducing the reaction barrier for the formation of HO₂+HCl, whereas it has a positive influence in Channel RW3. Additionally, to estimate the importance of these processes in the atmosphere, their rate constants were evaluated using conventional transition state theory with the Wigner tunneling correction. The result shows that the rate constant for the naked H₂O₂+Cl reaction is 1.60×10^-13 cm³ ·molecule^-1 ·s^-1 at 298.2 K, which is in good agreement with experimental values. Although the rate constant of channel RW3 is predicted to be 46.6-131 times larger than that of the naked H₂O₂+Cl reaction, its effective rate constant is smaller by 10-14 orders of magnitude than that of the naked reaction, that is, for the H₂O₂ + Cl reaction the naked reaction almost exclusively occurs under tropospheric conditions.

The hybrid density functional theory (DFT) methods M062X and X3LYP with the TZVP and 6-311++G(2d, p)+LANL2DZ basis sets were used to calculate the complexes formed between fifteen proline (Pro) conformers and Zn^2+/1+/0. The geometrical structures, energetics, vibrational frequencies, and electronic structures were investigated in detail. We obtained 19, 21, and 24 stable complexes for Pro-Zn^2+/1+/0 at the four levels. The most stable Pro-Zn²⁺ structure was a four-membered ring with Zn²⁺ bound to both oxygen ends (OO) of the zwitterionic proline, and the next stable compound was a five-membered ring with Zn²⁺ coordinated to both the amino nitrogen and carbonyl oxygen (NO) of proline, but Zn⁺ showed opposite behavior. The relative energy difference and the deformation energy of coordinated Pro decreased gradually with a reduction in the charge number of Zn. The binding energy of the Pro-Zn^2+/1+/0 systems are in the -620 to -936, -139 to -325, and -1.5 to -22 kJ·mol^-1 ranges, respectively. The properties of the Pro-Zn²⁺ system were significantly different when using different methods and basis sets. Both cationic systems indicated some charge transfer from Pro to Zn. The energy difference values for the frontier orbitals of all the complexes are lower than those of the corresponding fragments.

Heterocyclic molecules play a crucial role in health care and in pharmaceutical drug design. A large number of drugs used in Western medical practice are heterocyclic molecules. In this study, a set of norm indexes of the extended distance matrix are proposed. From these a stable and accurate structureproperty relationship model was developed for the prediction of the aryl hydrocarbon receptor binding affinity (pEC₅₀) of dibenzofurans and the mutagenic potency (lnR) of aromatic and heteroaromatic amines. Our results indicate that the new model, based on these norm indexes, provides very satisfactory results, and that the average absolute differences for pEC₅₀ prediction and lnR prediction were 0.403 and 0.702 with r² (square correlation coefficient) values of 0.876 and 0.779, respectively. A comparison of these results with other methods demonstrates that our method, based only on the same mathematical model, performed better in terms of both accuracy and stability.

Folding rate prediction plays an important role in clarifying the protein folding mechanism. In this work, we collected 115 protein samples with known folding rates including two-, multi-, and mixed-state proteins. To characterize the primary structure information of the protein molecules more comprehensively, we considered sequence length, residue components with different scales, k-space features for pair residues, and geostatistics association features among different locations of the residues substituted with corresponding physical-chemical properties. Each protein sequence was represented by a numeric vector containing 9357 numbers. We selected 23 features with a clear meaning from the above-mentioned high-dimensional features for each sample, after conducting an improved binary matrix shuffling filter and a worst descriptor elimination multi-round method. We constructed a nonlinear support vector regression (SVR) model based on the folding rate and the 23 retained features. The correlation coefficient of the Jackknife cross validation was 0.95. Our prediction accuracy was superior to other results from the literature and other reference feature selection methods. Finally, we established an interpretability system for SVR, and our data showed that the nonlinear regression relationship between the folding rates and the reserved features was highly significant. By further analyzing the effects of each retained descriptor on protein folding rates, the results showed that the protein folding rate might be closely related to the sequence length, the features associated with the medium-and short-range, the triplet residues component features, etc.

The aim of this study was to construct a quantitative structure-property relationship model to identify relationships between the molecular structures and viscosities of 310 compounds, as well as specific structural factors that could affect the viscosities of the compounds. Using an iterative self-organizing data analysis technique, the sample set was preliminarily classified into two sets, including a training set and a test set. The molecular structure descriptors of 310 compounds were calculated using version 2.1 of the Dragon software and subsequently sifted using an ant colony algorithm (ACO), which resulted in the selection of five parameters. Multiple linear regression (MLR) and the support vector machine (SVM) techniques were then used to establish ACO-MLR and ACO-SVMmodels, respectively. The results showed that the performance of the non-linear ACOSVMmodel (correlation coefficient R_train²=0.9013, R_test²=0.9026) was superior to the linearACO-MLRmodel (R_train²=0.7680, R_test²=0.8725). The correlation coefficients between the experimental and predicted values of the ACOMLR and ACO-SVM models for the test set were 0.934 and 0.950, respectively. The predictive properties of the two models were therefore determined to be satisfying. The application domain of the model was also studied using a Williams graph, which demonstrated that the models established in this study provide effective methods for predicting the viscosities of specific compounds based on their molecular structure.

Surfactants can be adsorbed with extracellular polymeric substances (EPS) to form micelles with the release of both free and bound water molecules, and this process could be used to improve the performance of the sludge dewatering process. In this paper, coarse-grained molecular dynamics (MD) simulations were adopted to study the formation and structure of complexes resulting from the mixing of a Gemini surfactant and EPS. The hydrophobic or hydrophilic performance of the polyelectrolyte had a significant impact on the adsorption process. The main driving force for adsorption between the hydrophilic polyelectrolyte and the Gemini surfactant was electrostatic attraction, where the head group of the Gemini surfactant was adsorbed onto the chain with the tail chain pointing towards the solvent. The adsorption process between the hydrophobic polyelectrolyte and the Gemini surfactant was influenced by both electrostatic and hydrophobic effects, with the Gemini surfactant being oriented parallel to the configuration of the polyelectrolyte chain. The coupling group length of the Gemini surfactant had very little influence on the adsorption process. Variations in the charge density of the polyelectrolyte chain aided the adsorption of the hydrophilic polyelectrolyte, but had no impact on the adsorption of the hydrophobic polyelectrolyte.

The mechanism of the Ni-catalyzed reductive cross-coupling reaction of bromobenzene (R₁) and methyl 4-bromobenzoate (R₂) to form an unsymmetrical biaryl system has been theoretically investigated using density functional theory calculations. Our results showed that the Ni⁰-catalyzed process was favored over the NiI-catalyzed mechanism. The mechanism for the reaction of the Ni⁰ catalyst initially attacking either R₁ or R₂ was quite similar, where the energy barrier in the gas phase for the rate-limiting step was 70.50 or 49.66 kJ·mol^-1, respectively. The mechanism in the favored Ni⁰-catalyzed reaction involved the following steps: first oxidative addition, reduction, second oxidative addition, reductive elimination, and catalyst regeneration. Our calculated results also indicated that no organometallic reagents were produced in the reaction cycle.

The adsorption behavior of Pb(OH)⁺ on the basal octahedral (001) surface of kaolinite has been investigated using the Perdew-Burke-Ernzerhof generalized gradient approximation (GGA-PBE) of density functional theory with periodic slab models, where the water environment was considered. The coordination geometry, coordination number, preferred adsorption position, and adsorption type were examined, with binding energy estimated. All the monodentate and bidentate complexes exhibited hemi- directed geometry with coordination numbers of 3-5. Site of "Ou" with "up" hydrogen was more favorable for monodentate complex than site of "O_l" with "lying" hydrogen. Monodentate complexation of "O_u" site with a high binding energy of -182.60 kJ·mol^-1 should be the most preferred adsorption mode, while bidentate complexation on "O_uO_l" site of single Al center was also probable. The stability of adsorption complex was found closely related to the hydrogen bonding interactions between surface O_l and H in aqua ligands of Pb(Ⅱ). Mulliken population and density of states analyses showed that coupling of Pb 6p with the antibonding Pb 6s―O 2p states was the primary orbital interaction between Pb(Ⅱ) and the surface oxygen. Hydrogen complexation occupied a much large proportion in the joint coordination structure of bidentate complex, where bonding state filling predominated for the Pb―O_l interaction.

The influence of molecular rotation, laser pulse shape and initial phase on controlling the infrared multiphoton excitation of diatomic molecules has been studied using an analytical algebraic approach, which involved the derivation of analytic transition probabilities with various rotational channels. To observe the correctional functions of the rotational energy and the relationship between the molecular orientation and the polarized direction of the laser field in terms of their impact on controlling multiphoton excitation, we calculated the probabilities in the purely vibrational and ro-vibrational cases. The maximumtransition probabilities were determined as a function of the time and molecular orientation angle in both cases for comparison, which allowed for the target multiphoton excitations to be achieved. However, oscillations appeared in the population of the ro-vibrational case which denoted rotational interference can decrease the selectivity of the molecular vibrational excitation. Furthermore, the rotational energy had a corrected action on multiphoton non-resonant excitation and the power of actions was dependent on the molecular anharmonicity. We have also provided a discussion of the influences of laser pulse shape and initial phase. We found that the use of an appropriate laser pluse shape afforded the target multiphoton excitation event, and that the initial phase of the chirped laser pulse had an obvious modulatory function on the multiphoton processes.

In this study, we performed a first-principles investigation of the rules governing changes in the electronic structure, band structure, optical properties, elastic properties, and anisotropy of an α-S₈ photocatalyst after carbon doping. It was shown that the bond length decreased, and the bond overlap population and charge density increased, with the formation of new C―S bonds, after doping. This indicated that the new bonds had enhanced covalence. The energy band gap of the doped structure was 2.64 eV, which is 0.15 eV lower than that of pure α-S₈, showing that doping increased the conductivity of α-S₈. The optical absorption spectrum of the doped system was extended to 650 nm, showing that the light absorption efficiency of α-S₈ was greatly enhanced. Calculations of the elastic properties showed that the mechanical capacity of carbon-doped α-S₈ decreased, but it remained brittle. The doped material had higher anisotropy.

The ground and excited states, charge- transport, and fluorescence properties of a series of polymers based on benzothiadiazole and silafluorene were investigated using density functional theory (DFT). The band gaps, ionization potentials, electron affinities, the lowest excitation energies, and absorption spectra of the polymers were estimated by extrapolating those of the oligomers to infinite chain lengths. The results show that the hole/electron injection/transport abilities and the optical properties of the polymers are significantly affected by the position of the benzothiadiazole group on the silafluorene group and the position of the butyl group on the thiophene group. (SiF2-DHTBT1-m)_n and (SiF1-DHTBT1-m)_n [hereafter SiF and DHTBT are silafluorene and 4,7-di(2-thienyl)-2,1,3-benzothiadiazole, respectively] show good hole and electron injection performances but (SiF1-DHTBT1-o)_n and (SiF1-DHTBT1-p)_n exhibit poor carrier injection performances. The predicted emission spectra of the polymers are located in the red visible-light range, except in the case of (SiF1-DHTBT1-o)_n.

Predicting the reactivity of electrophilic substitution at different sites is of theoretical and practical significance, and many prediction methods based on the electronic structure of reactants have been proposed. We compared the reliability of 14 prediction methods, using 14 monosubstituted and 8 disubstituted benzenes as test sets. Methods reflecting local electronic softness, such as the Fukui function and average local ionization energy, are well-suited to monosubstituted benzenes with ortho-para directing groups and disubstituted benzenes. However, these methods often fail for systems containing a single meta directing group. Methods reflecting electrostatic effects perform worse overall than those reflecting local softness, but are better suited to systems containing a single meta directing group. Dual descriptor is the most overall robust method, and can be regarded as a universal prediction method.

Density functional theory (DFT) calculations were used to study the adsorption of noble metal (Pt) on deprotonated 1,3-dipolar cycloaddition graphene to explore the mechanism of the formation of metal nanowires. The results show that: (1) Pt atoms that adsorb on 1,3-dipolar cycloaddition graphene induce the deprotonation of this 1,3-dipolar cycloaddition graphene and then the configuration changes to a deprotonated 1,3-dipolar cycloaddition graphene; (2) the noble metal anchoring site on the deprotonated 1,3-dipolar cycloaddition graphene is the ortho-carbon of nitrogen in the deprotonated pyridine alkyne, which was further confirmed by the average Bader charge of the ortho-carbon, and the average Bader charge of the ortho-carbon is as high as 1.0e; (3) Pt_n nanowire can form between two neighboring deprotonated pyridine alkyne units of deprotonated 1,3-dipolar cycloaddition graphene, and the Pt_n (n=3-6) nanowire adsorption configurations are more stable than the corresponding Pt_n (n=3-6) cluster adsorption configurations; and (4) the electronic structure analysis of the composite shows that Pt metal adsorption does not essentially change the electronic property of deprotonated 1,3-dipolar cycloaddition graphene. The doped states of the Pt metal result in the Pt₆ cluster adsorption composite being metallic while the doped states result in the Pt6 nanowire adsorption composite being semimetallic.

A dissipative particle dynamics simulation was performed to study the influence of blending different linear triblock copolymers A_xB_yC_z and linear diblock copolymers A_mB_n in an aqueous solution on the morphology diversity of the formed multicompartment micelles. The chain lengths of the linear triblock copolymers and diblock copolymers were varied to find the conditions of the formation of multicompartment micelles. The multicompartment micelle morphologies formed by the different blends of linear triblock copolymer and linear diblock copolymer are various, such as "worm-like" micelles, "hamburger" micelles, "sphere on sphere" micelles, and "core-shell-corona" micelles etc. Controlling the overall morphology and inner structure of the multicompartment micelles was possible using binary blends of a linear triblock copolymer and a diblock copolymer. The density profiles and the pair distribution function were calculated to characterize the structures of the obtained multicompartment micelles. In this work, by blending a linear triblock copolymer and a linear diblock copolymer, complex multicompartment micelles were prepared and characterized. This work shows that simply blending linear triblock copolymers and linear diblock copolymers is an effective way to control the morphology and structure of multicompartment micelles. This is more economical and easy to form multicompartment micelles in the engineering experiments. Therefore, the blending of copolymers should be given more attention in future for the design of new multicompartment micelles.

An all-atom force field was developed and validated for three energetic materials 1,3,5-triamino-2,4,6-trinitrobenzene (TATB), 1,3,5-trinitroperhydro-1,3,5-triazine (RDX), and octahydro-1,3,5,7-tetranitro-1,3, 5,7-tetrazocine (HMX). The functional form of the force field is widely used. The valence parameters were derived by fitting the quantum mechanics data. The atomic charge and van der Waals (VDW) parameters were optimized by fitting experimental data such as densities and sublimation enthalpies of the molecular crystals. The force field was validated by calculating the molecular conformers in the gas phase and the physical properties of the molecular crystals. It is demonstrated that the force field performs well in predicting molecular structures, vibrational frequencies, lattice parameters, crystalline densities, and sublimation enthalpies. Further validation showed that the force field predicts the equation of states and the bulk modulus well.

The aggregate morphology of rod-coil-rod copolymers in a dilute solution was investigated by dissipative particle dynamics simulations. The influences of the mutual compatibility between rod and coil blocks, the solvent property, the coil length, and the copolymer concentration on the aggregate structure were studied in detail. The simulation results show that the increase of the mutual compatibility between rod and coil blocks induces transformation of the aggregate morphology from spherical, to onion-like, to cage-like, and ultimately to cylindrical. With the increase in the hydrophobicity of the coil block, the cagelike aggregate changes into an onion-like aggregate, then a patchy aggregate, and then an inverted onionlike aggregate. Finally, a phase diagram of the rod-coil-rod triblock copolymers as a function of the coil length and the copolymer concentration is presented. It shows that cage aggregates are easily formed when the coil length is long and the concentration is relatively low, whereas onion-like aggregates are preferred when the coil length is short and the concentration is moderately low.

The effects of the diffusive (D_s(γ)=D₀×s^γ) and sticking (P_ij(σ)=P₀×(i×j)^σ) models on the colloidal suspension evolution, cluster-size distribution and scaling, time dependence of weight-averaged cluster size, and the fractal dimensions of aggregates are investigated. Simulations of the aggregation kinetics are carried out for a wide range of diffusivity exponent γ and sticking-probability exponent σ values. γ<0 and σ >0 have similar effects on the colloidal aggregation kinetics. The mechanism of transition from slow to fast aggregation is quantitatively analyzed. The physical significance of a cluster-cluster aggregation model, leading to a diffusion-limited aggregation model, is proposed. γ >>0 corresponds to the directional movement of clusters or primary particles, rather than random Brownian motion. The driving force for this directional movement may be a strong long-range van der Waals force, electric force of the largest cluster, or external force from the boundary. σ<<0 decreases the aggregation velocity of colloidal particles, with the evolution of the colloidal suspension. This may correspond to the largest cluster being a repulsive center, and a repulsive force existing between clusters or primary particles. The simulation confirms particle aggregation involving the weight-averaged size growing exponentially at first, but obeying a power law later. The aggregation kinetics is a positive-feedback nonlinear process as σ >0, but a negative-feedback process as σ<0.

We have designed a family of novel molecules BX[(CH₂)_n]₃ and BX(CH₂)[CH(CH₂)_nCH] (X=N, P) with the [n.n.n]propellane configuration (n=1-6). The structures, stabilities, chemical bonds, and electronic spectra of these structures were investigated using density functional theory (DFT). The calculated results indicate that all of these compounds are situated at minima on the potential energy surfaces. The energy gaps between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of BN[(CH₂)_n]₃ and BP[(CH₂)_n]₃ (n=1-6) were in the range of 5.24-7.07 eV and 5.47-7.33 eV, respectively, and the energy gap of BX[CH₂]₃ is close to that of C₅H₆. In addition, the energy gaps of BN(CH₂) [CH(CH₂)_nCH] and BP(CH₂) [CH(CH₂)_nCH] (n=1-6) are around 6.80 eV. To compare the relative stabilities of these compounds, we investigated the second-order differences of energies. The results indicate that BN[(CH₂)₃]₃, BP[(CH₂)₄]₃, and BX(CH₂)[CH(CH₂)₂CH] (X=N, P) are more stable than the other structures. Moreover, based on the bond lengths, Wiberg bond indices, and charges of the two"inverted"atoms, it can be concluded that the bridgehead B and N(P) atoms in BN[(CH₂)_n]₃ (n=2, 6) and BP[(CH₂)₂]₃ do not form chemical bonds, while the two bridgehead atoms in the other compounds studied formed chemical bonds. Additionally, topological analysis of the electron density using the theory of atoms-in-molecules shows that the inverted N―B bonds in BN[(CH₂)_n]₃ (n=3-5) are ionic bonds whereas the B―P bonds in BP[(CH₂)_n]₃ (n=3-6) have covalent character. The vertical transition energies of BN[(CH₂)_n]₃, BP[(CH₂)_n]₃, BN(CH₂) [CH(CH₂)_nCH], and BP(CH₂) [CH(CH₂)_nCH] (n=1-6) range from 191.1 to 284.8 nm, 191.8 to 270.1 nm, 190.5 to 199.7 nm, and 209.0 to 221.3 nm, respectively.

In this work, we investigate the low-lying states of PbS, PbSe, and PbTe cations based on a recently developed equation-of-motion coupled-cluster approach for ionization potentials (EOMIP-CC) with spin-orbit coupling (SOC) at the CCSD level. Equilibrium bond lengths, harmonic frequencies as well as vertical and adiabatic ionization energies are calculated with EOMIP-SOC-CCSD and reasonable agreement with available experimental data is achieved. The contribution of triples is estimated by comparing results at the CCSD(T) level with those from EOMIP-CCSD when SOC is neglected. Better agreement with experimental data can be obtained if the contribution of triples is included. According to our results, the splitting between ²Π state is larger in PbTe⁺ than that in PbS⁺ and PbSe⁺, while coupling between ²Π_1/2 and ²Σ_1/2 owing to SOC is more significant in PbS⁺ and PbSe⁺. This is because the energy difference between ²Π and ²Σ⁺ states of PbTe⁺ is larger than that in PbS⁺ and PbSe⁺ and the SOC matrix element between ²Π_1/2 and ²Σ_1/2 states in PbTe⁺ is only half those in PbS⁺ and PbSe⁺. The present work presents new estimates on properties of these low-lying states and could serve as new references for future experiments.

We investigated the ground and excited state electronic properties of finite length zigzag graphene nanoribbons, using time-dependent density functional theory. The ground state of short graphene nanoribbons with eight Hatoms on their armchair edges (8-ZGNR) is diamagnetic, and antiferromagnetismcan be exhibited with increasing the length of nanoribbons. The antiferromagnetismand half-metallicity can also be shown when a static field is added. When a laser pulse is applied in the excited state, the induced electrons can move and change with the laser pulse. There exist some differences between α- and β-spin electrons. α-Spin electrons can be induced, and showinduced charge density more readily. β-Spin electrons can escape the external field control, and show non-adiabatic properties more readily.

ReaxFF molecular dynamics simulations of trinitrotoluene (TNT) pyrolysis show that use of the ReaxFF/lg potential function, which adds the London dispersion term, gives superior results in equilibrium density calculation of energetic materials. According to our calculations using limited time steps, the main products are NO₂, NO, H₂O, N₂, CO₂, CO, OH, and HONO, and H₂O, N₂, and CO₂ are the final products. We also used ReaxFF potential functions to simulate the same process to conduct a comparative analysis. The main and final products are consistent with those obtained using ReaxFF/lg, but the kinetics are different. Both ortho-NO₂ homolytic cleavage and C―NO₂→C―ONO rearrangement homolysis are thermodynamically favorable pathways in the early thermal decomposition of TNT. However, C―NO₂→C―ONO rearrangement homolysis is less favorable kinetically than C―NO₂ homolysis, since C―NO₂ is the weakest bond in TNT. Soon after their formation, NO₂ and NO participate in secondary reactions and eventually form N₂. Pyrolysis to form OH and other small molecules promotes the formation of H₂O. Aromatic ring fission does not take place until most of the attached groups have interacted or are removed, and increasing the temperature accelerates main-ring fission and further decomposition to form CO₂; this is the major reason for CO₂ distribution fluctuations under high-temperature conditions. When the TNT molecules in the unit cell are almost completely decomposed, the potential energy of the system is significantly attenuated. The maximum amount of carbon-containing clusters formed in the thermal decomposition is more dependent on density than on temperature. Moreover, the simulation results show that coagulation of carbonaceous intermediates occurs before the TNT decomposes completely. These studies show that the simulation of TNT pyrolysis using the ReaxFF/lg reactive force field can provide detailed kinetic and chemical information, which are helpful in understanding the detonation of energetic materials and assessing their security.

Clay minerals are used to remove organics and to remediate soils and groundwater contaminated with petroleum hydrocarbons. Cluster models of Si₆O₁₈H₁₂ and Al₆O₂₄H₃₀ for the tetrahedral (Si―O) and octahedral (Al―O) surfaces of kaolinite were set up to mimic kaolinite surfaces. The interactions of benzene molecule and the kaolinite cluster models were systematically studied at the MP2/6- 31G(d,p)//B3LYP/6-31G(d,p) level. The gas- state adsorption properties of benzene on the kaolinite surfaces, such as the optimized structures, structural parameters, adsorption energies, natural bond orbital charge distributions, vibration frequencies, electrostatic potential maps, electron density characteristics (the ρ and ▽²ρ values of secondary hydrogen-bonds), and electron density difference, were analyzed in this work. The optimized structures indicate that the adsorption of benzene molecule on the kaolinite surfaces may be caused by formation of secondary hydrogen-bonds. The results for the other properties further confirmed the existence of secondary hydrogen-bonds. Benzene molecule is more likely to be adsorbed on the Al―O surface than on the Si―O surface. The adsorption angle between the benzene ring plane and the kaolinite Al―O surface is about 90°.

As an unconventional gas, coalbed methane (CBM) is a desirable alternative energy source to conventional fossil fuels such as coal, oil, and natural gas. In this work, non-metallic atom X (X=H, O, N, S, P, Si, F, or Cl)- decorated Gr (graphene) (X-Gr) was used to represent the surface models of coal with structural heterogeneity. Using density functional theory, the adsorption of the CBM component Y (Y=CH₄, CO₂, H₂O) on X-Gr was systematically investigated. The results indicate that CH₄, CO₂, and H₂O are weakly bound to X-Gr, and the interactions between the adsorbate and the surface can be described as physisorption, which was identified through the density of states and electronic density difference analysis. Furthermore, CH₄ has very large adsorption energies to H- and Cl-decorated graphene. The dopants X, such as N, O, F, and Cl, are very good adsorbents for CO₂ and the influence of the dopants N and Cl cannot be ignored for the adsorption of H₂O. In general, the adsorption energies of H₂O on X-Gr are larger than those of CO₂, while CH₄ has the lowest adsorption energies, namely, the order of adsorption is H₂O> CO₂>CH₄. Consequently, the injection of H₂O or CO₂ into methane-rich coal seams strongly enhances the CBM recovery efficiency via competitive adsorption with CH₄ on the coal surface. The results provide a molecular-level insight into the interactions between CBM and X-Gr, and might offer useful information for recovery and purification of coalbed methane.

The effects of the first hydration shell and the bulk solvation effects on the proton-transfer processes of guanine-cytosine (GC) and adenine-thymine (AT) base pairs are studied based on density functional theory, using the B3LYP method and DZP++ basis set. The proton-transfer mechanisms of the GC and AT base pairs in bulk solvation are first single-proton transfer (SPT1) and stepwise double-proton transfer (DPT). When only the first hydration shell surrounded by five water molecules (GC ·5H₂O, AT· 5H₂O), or both the first hydration shell and bulk solvation effects through polarizable continuum model (PCM) (GC·5H₂O+PCM, AT·5H₂O+PCM) are considered, only the first single-proton-transfer mechanism (SPT1) is found. The proton- transfer activation energies of the GC and the AT base pairs show that the majority of the hydration effects come from the first hydration shell through hydrogen- bond interactions, therefore the first hydration shell greatly influences the base pair structures and proton-transfer mechanism.

The axial coordination behavior of the 5,10,15-tris(pentafluorophenyl)corrole manganese [(TPFC)Mn^Ⅲ] and 5,10,15-tris(pentafluorophenyl)corrole manganese(V)-oxo [(TPFC)Mn^VO] complexes with N-based ligands, such as imidazole, methylimidazole, isopropylimidazole, and pyridine, were investigated using density functional theory (DFT) at BP86 level. The results show these N-based ligands can form a stable axial coordination complex with (TPFC)Mn^Ⅲ in its quintet state. The coordination binding strength followed the order imidazole>4-methylimidazole>pyridine, which is in agreement with experimental results. The binding energy and the large distance between the Mn and N atom of the ligands indicates that (TPFC)Mn^VO cannot form an effective coordination bond in its singlet or triple state. Natural bond orbital (NBO) analysis indicates that the 3d orbitals of the Mn atom in (TPFC)Mn^VO are fully occupied, and there are no empty 3d orbitals to accept lone pair electrons from the ligands. However, there is a weak coordination interaction between the ligands and (TPFC)Mn^VO in its triplet state.

To investigate the effect of a tetrathiafulvalene (TTF) unit on the photovoltaic properties of the corresponding dye sensitizer, a TTF-carbazole-based sensitizer, Dye 2, was designed; it was based on the framework of Dye 1. The geometries, electronic structures, and optical properties of Dye 1 and Dye 2 before and after binding to (TiO₂)₉ clusters were investigated using density functional theory (DFT) and timedependent DFT. The surface morphologies of the dyes on TiO₂ (101) surfaces were simulated by periodic DFT calculations using the DMol³ program. The calculated results showed that the introduction of TTF units into dyes could help to inhibit dye aggregation on the TiO₂ surface; this is conducive to intramolecular charge- transfer transitions and significantly improves the light-harvesting ability. The calculated results demonstrate that the TTF unit is a very promising electron donor for improving the photovoltaic properties of organic dye sensitizers.

The electronic structures and optical properties of the nine poly(vinyldene fluoride) (PVDF) crystalline forms are calculated by the first-principles method based on density functional theory with inclusion of the Tkatchenko-Scheffler (TS) dispersion corrections. The nine crystalline forms of PVDF are insulators with band gap energies from6.05-7.34 eVat zero pressure and zero temperature. The calculated results of the band gap energy of the Ⅰ_p (β) and Ⅱ_ad crystalline forms are close to other experimental data or calculated results. The energy bands of PVDF crystals are dense and straight. The valence bands consist mainly of F-2s and F-2p states and the conduction bands are dominated by C-2p and H-1s states. In the 0-35 eV photon energy range, the optical properties, such as dielectric function, absorption, reflectivity and refractive index, primarily change in the deep ultraviolet region in our calculations. According to the spectra features (spectral range, peaks, etc.) of the optical properties, the nine crystalline forms of PVDF can be divided into four categories: {Ⅰ_p}, {Ⅱ_pu}, {Ⅱ_au, Ⅱ_ad, Ⅱ_pd, Ⅲ_pu}, {Ⅲ_au, Ⅲ_ad, Ⅲ_pd}. The crystalline forms in each category have similar spectra features.

The structural stability and mechanical properties of α-Nb₅Si₃ alloyed with Ti, Cr, Al and B were investigated using first- principles methods based on density functional theory (DFT) by comparing the formation energy, valence electron concentrations, elastic constants, the shear modulus/bulk modulus ratio, and the Peierls stress. The results show that the structures of the α-Nb₅Si₃ alloys retain the stable D8₁ structure, in which the alloying elements Ti, Cr, Al and B prefer to occupy the Nb^4c, Nb^4c, Si^4a and Si^8h sites of α-Nb₅Si₃, respectively. The addition of Ti, Al and B increase the brittleness of D8₁ structured α-Nb₅Si₃, while Cr addition is beneficial to the toughness of α-Nb₅Si₃. Moreover, the influence of the alloying elements on the ductility/brittleness of α-Nb₅Si₃ was investigated based on analysis of the electronic structure, density of states and Mulliken population. The increased brittleness of α-Nb₅Si₃ by the addition of Ti, Al and B can be attributed to enhanced orientation of the covalent bonds, whereas Cr addition weakens the number and strength of covalent bonds and more anti-bonding states are occupied, thus improving the toughness.

The effects of proton transfer on the reaction between 2,4-diisocyanatotoluene (2,4-TDI) and active-hydrogen-containing amine compounds were calculated using density functional theory (DFT) at the B3LYP/6-31+G(d, p) level. The energy barriers are significantly reduced when a methanol molecule serves as a proton transporter or a reactive catalyst, indicating that the labile hydrogen-containing compound plays a key role in accelerating the reaction rate and proton transfer. The catalytic addition of 2,4-TDI and methyl N-methylcarbamate follows a one-step mechanism, with a transition state characterized by a sixmembered ring. However, the catalytic additions of 2,4-TDI and aromatic amines such as N-methyl-p-nitroaniline, diphenylamine, and 1,2-dihydro-2,2,4-trimethylquinoline involve two steps, with the first step as the rate-limiting step. The reactions between 2,4-TDI and aromatic amines have lower energy barriers than that between 2,4-TDI and methyl N-methylcarbamate. The aromatic amines are more active than methyl N-methylcarbamate in the reaction with 2,4-TDI, which is in a good agreement with experimental results.

Some properties of g-C₃N₄ with carbon positions doped by B, P, and S atoms were investigated using quantum mechanics (first principles). There are two symmetric carbon atoms in g-C₃N₄, named C1 and C2. C1 is easier to dope than C2, and the system doped at C1 is more stable. It was found that it is easier to dope g-C₃N₄ with B than with P and S. There are significant differences among the crystal structures after doping, this is attributed to the sizes and electronegativities of the different doping atoms. The orbital population distributions showed that the electronic valences of the B, P, and S atoms changed when the doping was changed. This shows that hybrid doped atoms linked with adjacent atoms through covalent bonds are present. The differences between the valence electrons of the dopant atoms and the substituted atoms result in new bands after doping. The emergence of a new energy band in the band gap of the original g-C₃N₄ results in a decreased band gap after doping, indicating that the conductivity of the doped system is higher than that of the non-doped system. Analyses of the optical properties of pure g-C₃N₄ and doped g-C₃N₄ show that the optical absorption spectrum of g-C₃N₄ is mainly in the ultraviolet region, and the wavelength range of light absorption is unchanged after doping with P and S. However, after doping with B, the wavelength range of light absorption extends to the visible and infrared regions. Strong absorption in the infrared region shows that the photocatalytic activity of g-C₃N₄ after doping with B is much higher than that of undoped g-C₃N₄. The electron energy loss spectrum, optical conductivity spectrum, and the dielectric function curve support these points.

We investigated the effect of alkali-metal-atom doping on the electronic transport properties of BDC60 molecules, using a combination of first-principles density-functional theory and the non-equilibrium Green's function. Our calculation results show that alkali-metal-atom-doped BDC60 molecules exhibit good rectifying and negative differential resistance behaviors at very low bias. The intrinsic mechanisms for these phenomena are discussed systematically in terms of the transmission spectra and frontier molecular orbitals, as well as their spatial distributions under various external applied biases. Our study will help in developing future applications of BDC60 molecules in low-bias rectifying and negative differential resistance molecular devices.

The electronic structures and optical properties of 4-N,N-dimethylamino-4'-N'-methylstilbazolium tosylate (DAST) and 4-N,N-dimethylamino-4'-N'-methylstilbazolium 2,4,6-trimethylbenzenesulfonate (DSTMS) were investigated using density functional theory based on the plane wave basis set. The results indicated that the two compounds showed similar band structures, and the top of the valence band and the bottom of the conductive band mainly originated from the N 2p states of dimethylamino and methylpyridine, respectively. In terms of the linear optical properties, the birefringence indexes, Δn, of the two compounds were very large (Δn>0.5), and they exhibited good light transmission in the mid-and far-infrared regions. With regard to second-order nonlinear optical characteristics, the DAST and DSTMS crystals showed strong second harmonic generation (SHG) responses, and the corresponding SHG coefficients (d₁₁) were about 150 pm·V^-1. Analysis of the band structures showed that the SHG responses of the two compounds were closely related to charge transfers between electron-donating and electron-withdrawing groups. Ethylene bridging also played an important role in the charge transfer process.

The geometries, polarizabilities (α_s), and first hyperpolarizabilities (β_tot) of a series of green fluorescent protein chromophore coupled diradicals and their corresponding optical isomers were investigated using density functional theory (DFT). The results show that the introductions of the electron donor/acceptor significantly enhance the polarizabilities and have a different influence on the first hyperpolarizabilities. For trans isomers, the β_tot values of the studied compounds increase with increasing strength of the electron-withdrawing ability of the substituent, whereas the β_tot values decrease significantly with increasing strength of the electron-donating ability of the substituent. For cis isomers, the trends in the changes in the β_tot values are the opposite of those for trans isomers on introduction of a donor/acceptor. Significantly, photoisomerization can lead to the different β_tot values. The β_tot values of cis isomers are smaller than those of trans isomers when electron acceptors are introduced. For example, the β_tot value of the cis isomer with the strongest electron acceptor, i.e., ―NO₂, is about 1/6 that of the corresponding trans isomer. However, the β_tot values of trans isomers are smaller than those of cis isomers when electron donors are introduced. For example, the β_tot value of the trans isomer with the strongest electron donor, i.e., ―NH₂, is about six times smaller than that of the corresponding cis isomer. As a result, photoisomerization can modulate the molecular nonlinear optical (NLO) responses effectively.

A detailed understanding of how nucleobases interact with protein peptides will allow us to gain valuable insights into how these interesting biological molecules could be used to construct complex nanostructures and materials. In this work, the optimal structures and binding energies of 20 hydrogenbonded complexes, which contained the nucleic acid base adenine, N-methylacetamide, a glycine dipeptide, and an alanine dipeptide, were obtained. The site preferences of adenine hydrogen bonding to peptide amides were explored. The calculation results show that adenine can use two binding sites (site A1 and site A2) to form N―H…N or N―H…O=C hydrogen-bonded complexes with N-methylacetamide; the N―H…N hydrogen-bonded complexes formed at site A1 of adenine are more stable. The calculation results also show that the glycine dipeptide can use either site Gly7 or site Gly5, and the alanine dipeptide can use either site Ala7 or site Ala5 to form hydrogen-bonded complexes with adenine; the hydrogenbonded complexes formed at site Gly7 of the glycine dipeptide and at site Ala7 of the alanine dipeptide are more stable. The hydrogen-bonded complexes formed by adenine and a dipeptide have larger negative binding energies than the complexes formed by adenine and N-methylacetamide, indicating that the interaction between adenine and the peptide is preferred to that between adenine and N-methylacetamide. The nature of the hydrogen bonding in these complexes was further explored based on the atoms in molecules calculations and the natural bond orbital analysis.