镱硫属化合物的密度泛函理论研究

用密度泛函理论(DFT)研究镱硫属化合物的电子结构和性质,通过与实验比较考察了现有的几种近似密度泛函公式对镧系元素化合物的适用程度和相对论效应的影响.结果表明,用DFT计算的YbO键长对实验值的偏差约为0.002nm;但得到的键能即使在考虑梯度校正和相对论效应之后,仍比实验值高,在定域密度近似基础上引入交换梯度校正使键能计算值减小,其中PW86x使键能计算值减小稍多些,结果更接近实验值;相关梯度校正使键能计算值升高.相对论效应使键长缩短0.004～0.006nm,键能减小约0.5eV.计算结果的分析表明,Yb的5d轨道和配体的np轨道间形成σ键和π键.在所研究的分子体系中,配体原子从O到Te、Yb原子的5d轨道布后数依次减少,同键能减弱的顺序一致.相对论效应使键能减小的主要原因是在成键过程中发生了Yb的6s电子向5d轨道的转移,而相对论效应使该过程能量增加.偶极矩和电荷分布的计算表明,Yb-L键以共价性为主,相对论效应使共价性成份增加.

Study on Ytterbium Chalcogenides by Means of Density Functional Theory

The ytterbium chalcogenides have been studied by means of the density functional theory(DFT). The validity of the present approximate DFTformulas and the influence of relativistic effects for the lanthanide compounds have been examined by comparing the calcu-lated results with the experiments. The results show that the bond length of YbOobtained from DFTcalculations differs from the experimental value by about 0.002 nm- However,the bond energies are overestimated by DFT, even though both the gradient corrections and relativistic effects are taken into account. Introducing the exchange gradient coorrections on the basis of LDAcan reduce the calculated bond energies. Among the examined formulas for the exchange gradient correction, the formula PW86x produces a little lower energies and gives better results. The correlation correction increases the calculated bond energies. The relativistic effects make the bond lengths shorter by 0.004-0.006 nm, and make the bond energies lower by about 0. 5 eV. Analysis of the obtained results shows that the σ- and π-bonds are formed through the interaction between the 5d orbitals of Yb and the nPorbitals of the ligands. The populations in the 5d orbitals of Yb decrease through YbOto YbTe, fol-lowing the trend of the decrement of the bond energies. The relativistic effects destabilize the bonds, which may be due to the fact that the 6s electrons of Yb transfer to 5d orbitals in bond formation while the relativistic effects raise the energy of this process. The obtained dipole moments and charge distribution show that the bonds in ytterbium chalcogenides bear large covalence components which are increased by the relativistic effects.