Abstract: The geometries and electronic structures of methyl nitrate and its dimers have been calculated by DFT method at the B3LYP/631G level and ab initio method at the HF/631G level respectively.The total energies using 6311G and 6311＋＋G basis sets have been calculated.Dimer binding energies at the HF/631G level have been corrected for MP4SDTQ electron correlation.All the binding energies have been corrected by the basis set superposition error (BSSE) and zero point energies (ZPE).Based on the vibrational analysis,the changes of thermodynamic properties at 200～600 K temperatures from mono to dimer have been calculated using the statisticalthermodynamic method.It is found that DFT method gives shorter intermolecular distances in a dimer,larger bond lengths in a molecule,and much smaller binding energies than those given by ab initio method.

Key words: Methyl nitrate dimer, Intermolecular interaction, DFT(density functional theory), Ab initio, Thermodynamic properties