基于密度泛函理论方法的δ目Pu5f状态电子结构计算

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

为了描述5-Pu中5，电子的定域，离域状态，获得准确的5，电子布居数，本文采用多种密度泛函理论方法对5f（n=0—7）电子构型进行了第一性原理计算．研究结果表明，白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0．475nm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5，4和5f。电子构型以外，自旋极化广义梯度近A（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0．570nm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、5f、5f、5f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、5严f2、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．5，投影态密度表明自旋极化效应导致5，轨道产生交换劈裂行为，部分5，状态从Fermi能级上消失，降低5，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5，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方法计算获得的品格常数与实验值相当一致．

First-principle calculations of 5fn （n=0-7） electronic configurations are performed with several density functional theory （DFT） methods to describe the Iocalized/delocalized states and obtain the precise population of the 5f manifold in delta-plutonium （5-Pu）. The results show that spin polarization clearly reduces the cohesive energies of each electronic configuration, and enhances the cohesion properties. For 5f0, 5f1, 5f2, 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 5-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-GGA method, 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）＋U method, 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, 5P （5f4） electronic configurations are the same as that of the 5f7 （5f6） electronic configuration. The cohesive energies of 5f7 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 5forbitals. Several 5fstates are removed from the Fermi level, which lowers the contribution of 5fstates to chemical bonding, and enhances the lattice constant, indicating that strong spin polarization induces partial localization of 5forbitals. 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%）.