Physics Department, Central Michigan University, Mt. Pleasant, Michigan 48859, USA.
Physics Department and Science of Advanced Materials Program, Central Michigan University, Mt. Pleasant, Michigan 48859, USA.
J Chem Phys. 2019 Nov 7;151(17):174106. doi: 10.1063/1.5125205.
Spurious electron self-interaction in density functional approximations (DFAs) can lead to inaccurate predictions of charge transfer in heteronuclear molecules that manifest as errors in calculated electrostatic dipoles. Here, we show the magnitude of these errors on dipoles computed for a diverse set of 47 molecules taken from the recent benchmark study of Hait and Head-Gordon [J. Chem. Theory Comput. 14, 1969 (2018)]. We compare the results of Perdew-Wang local spin density approximation (PW92), Perdew-Burke-Ernzerhof (PBE) generalized gradient approximation (GGA), and strongly constrained and appropriately normed (SCAN) meta-GGA dipole calculations, along with those of their respective self-interaction-corrected (SIC) counterparts, to reference values from accurate wave function-based methods. The SIC calculations were carried out using the Fermi-Löwdin orbital (FLO-SIC) approach. We find that correcting for self-interaction generally increases the degree of charge transfer, thereby increasing the size of calculated dipole moments. The FLO-SIC-PW92 and FLO-SIC-PBE dipoles are in better agreement with reference values than their uncorrected DFA counterparts, particularly for strongly ionic molecules where significant improvement is seen. Applying FLO-SIC to SCAN does not improve dipole values overall. We also show that removing self-interaction improves the description of the dipole for stretched-bond geometries and recovers the physically correct separated atom limit of zero dipole. Finally, we find that the best agreement between the FLO-SIC-DFA and reference dipoles occurs when the molecular geometries are optimized using the FLO-SIC-DFA.
密度泛函近似（DFA）中的虚假电子自相互作用可能导致异核分子中电荷转移的预测不准确，表现为计算静电偶极子的误差。在这里，我们展示了这些错误在最近由 Hait 和 Head-Gordon 进行的基准研究[J. Chem. Theory Comput. 14, 1969 (2018)]中计算的 47 种不同分子的偶极子上的大小。我们比较了 Perdew-Wang 局域自旋密度近似（PW92）、Perdew-Burke-Ernzerhof（PBE）广义梯度近似（GGA）和强约束且适当归一化（SCAN）meta-GGA 偶极子计算的结果，以及它们各自的自相互作用校正（SIC）对应物，与来自精确波函数方法的参考值进行比较。SIC 计算是使用费米-洛温（FLO-SIC）方法进行的。我们发现，自相互作用的校正通常会增加电荷转移的程度，从而增加计算偶极矩的大小。与未校正的 DFA 对应物相比，FLO-SIC-PW92 和 FLO-SIC-PBE 偶极子与参考值更一致，特别是对于强离子分子，其改进更为显著。在 SCAN 中应用 FLO-SIC 总体上不会改善偶极子的值。我们还表明，去除自相互作用可以改善拉伸键构象的偶极子描述，并恢复物理上正确的零偶极子分离原子极限。最后，我们发现，当使用 FLO-SIC-DFA 优化分子几何形状时，FLO-SIC-DFA 和参考偶极子之间的最佳一致性发生。
