物理化学学报 >> 2015, Vol. 31 >> Issue (Suppl): 75-80.doi: 10.3866/PKU.WHXB2014Ac03

研究论文 上一篇    下一篇

基于密度泛函理论方法的δ相Pu 5f状态电子结构计算

李如松1, 何彬1, 李刚1, 许鹏1, 卢新城2, 王飞1   

  1. 1 第二炮兵工程大学核工程系, 西安710025;
    2 海军核化安全研究所, 北京100077
  • 发布日期:2015-05-20
  • 通讯作者: 李如松 E-mail:rusong231@126.com
  • 基金资助:

    国家自然科学基金(51401237, 51271198, 11474358)和第二炮兵工程大学基金(2014QNJJ018, YX2012cxpy06)资助项目

An Electronic Structure Calculation for 5f States of δ Phase Plutonium Based on the Density Functional Theory Method

LI Ru-Song1, HE Bin1, LI Gang1, XU Peng1, LU Xin-Cheng2, WANG Fei1   

  1. 1 Xi'an Research Institute of High Technology, Xi'an 710025, P. R. China;
    2 Navy Research Institute of Nuclear and Chemistry Safety, Beijing 100077, P. R. China
  • Published:2015-05-20
  • Contact: LI Ru-Song E-mail:rusong231@126.com
  • Supported by:

    The project was supported by the National Natural Science Foundation of China (51401237, 51271198, 11474358) and Self-Topics Fund of Xi'an Research Institute of High Technology under Contract, China (2014QNJJ018, YX2012cxpy06).

摘要:

为了描述δ-Pu中5f 电子的定域/离域状态, 获得准确的5f 电子布居数, 本文采用多种密度泛函理论方法对5fn (n=0-7)电子构型进行了第一性原理计算. 研究结果表明, 自旋极化效应明显降低各个电子构型的内聚能, 增强其内聚性质. 对于5f0、5f1、5f3、5f4、5f6电子构型, 当晶格常数超过0.475 nm时, 自旋极化局域密度近似(SP-LDA)+U方法计算获得的内聚能明显低于SP-LDA方法. 除了5f4和5f6电子构型以外, 自旋极化广义梯度近似(SP-GGA)+U方法计算获得的内聚能明显低于SP-GGA方法, 当晶格参数超过0.570 nm时, SP-GGA+U和SP-LDA方法计算的内聚能趋向于重合. 对于SP-LDA+U方法, 5f0、5f1、5f3、5f4和5f6电子构型的内聚能是相同的, 5f2、5f5和5f7电子构型的内聚能是相同的. 对于SP-GGA+U方法, 5f0、5f1、5f2、5f3、5f5和5f7电子构型的内聚能是相同的, 5f4和5f6电子构型的内聚能趋向于重合. 5f 投影态密度表明自旋极化效应导致5f 轨道产生交换劈裂行为, 部分5f 状态从Fermi 能级上消失, 降低5f 状态对化学成键过程的贡献, 增加了平衡体积, 即强烈的自旋极化效应导致5f 电子的"部分定域化". SP-GGA+U方法明显高估了晶格常数, 而SP-LDA方法计算获得的晶格常数与实验值相当一致.

关键词: 5f状态, 电子结构, 定域状态, 自旋极化

Abstract:

First-principle calculations of 5fn (n=0-7) electronic configurations are performed with several density functional theory (DFT) methods to describe the localized/delocalized states and obtain the precise population of the 5f manifold in delta-plutonium (δ-Pu). The results show that spin polarization clearly reduces the cohesive energies of each electronic configuration, and enhances the cohesion properties. For 5f0, 5f1, 5f3, 5f4, and 5f6 electronic configurations, the cohesive energies obtained by the spin- polarized local density approximation (SP-LDA)+U method are markedly smaller than that by the SP-LDA method when the lattice constant of δ-Pu exceeds 0.475 nm. The cohesive energies calculated with the spin-polarized generalized gradient approximation (SP-GGA)+U method are smaller than that by SP-GGAmethod, except for 5f4 and 5f6 electronic configurations, and the former trend to coincide with SP-LDA results when the lattice constants are larger than 0.570 nm. For the SP-LDA(GGA)+Umethod, the cohesive energies of 5f0, 5f1, 5f3, 5f4, and 5f6 (5f0, 5f1, 5f2, 5f3, 5f5, and 5f7) electronic configurations are all equal, while the cohesive energies of 5f2, 5f5 (5f4) electronic configurations are the same as that of the 5f7 (5f6) electronic configuration. The cohesive energies of 5fn electronic configurations calculated using the other methods are equal. 5f projected densities of states show that spin polarization results in the exchange split behavior of 5f orbitals. Several 5f states are removed from the Fermi level, which lowers the contribution of 5f states to chemical bonding, and enhances the lattice constant, indicating that strong spin polarization induces partial localization of 5f orbitals. The optimized lattice constants obtained by the SP-LDA method are in good agreement with the experimental values, but the SP-GGA+U method sharply overestimates the lattice constant (by up to about 20%).

Key words: 5f state, Electronic structure, Localization, Spin polarization

MSC2000: 

  • O641