几种密度泛函理论公式用于镧系硫属化合物计算的比较

Comparison of Several Density Functional Formulas by Application to Calculations of Lanthanide Chalcogenides

以镧系元素La、Gd、Lu的硫属化合物为对象，系统考察几种密度泛函理论公式对镧系化合物计算的适用情况，考虑了相对论效应的影响．计算结果显示，相对论效应引起的键长变化在十2Pm到-3Pm之间，引起的键能减小为0．4～0．6eV，与采用的密度泛函公式关系不明显．不同的密度泛函公式对键长的计算结果影响也不太大，但对键能有显著影响，其中LDA（VWN）＋PW86X公式给出最好结果．交换能梯度校正明显改善键能计算结果，而相关能梯度校正反而使之变差．简单的Xα公式给出相当好的键能计算结果．在考虑相对论效应和梯度校正以后，密度泛函理论方法给出比较可靠的键长数值，键能则仍然偏高，但不超过20％．

The applicability of several density functional formulas to theoretical calculationsof lanthanide chalcogenides has been investigated by per forming calculations on LnL(Ln=La, Gd, Lu 3 L=O, S, Se, Te). The influence of relativistic effects has been considered.The calculated results show that the relativistic effects result in variation of bond lengths from +2 pm to -3 pm, and result in bond energy decrease by 0- 4~O. 6 eV, and there is noobvious dependance on the adopted density functional formulas. The difference of densityfunctional formulas does not obviously affect the calculated bond lengths, but signifacantlyinfluence the calculated bond energies. It is found that LDA (VWN) +PW86x scheme givesthe best bond energy. The gradient correction of exchange energy obviously improves thecalculated bond energies, whereas the gradient correction of correlation energy worsen theresults, in consistency with previous conclusions. The simple Xa formula gives pretty goodcalculated bond energies. Taking the relativistic effects and suitable gradient corrections intoaccount,the density functional method gives satisfactory bond lengths, while the calculatedbond energies are still too high, although the relative deviation does not exceed 20%.