Hasebe Masatoshi, Tsutsumi Takuro, Taketsugu Tetsuya, Tsuneda Takao
Graduate School of Chemical Sciences and Engineering, Hokkaido University, Sapporo, Japan.
Department of Chemistry, Faculty of Science, Hokkaido University, Sapporo, Japan.
J Comput Chem. 2023 Dec 5;44(31):2391-2403. doi: 10.1002/jcc.27204. Epub 2023 Sep 1.
Total and orbital electron densities of molecules are explored for the effect of the long-range correction (LC) for density functional theory (DFT) exchange functionals by comparing to the effect of the ab initio coupled cluster singles and doubles (CCSD) method. Calculating the LC effect on the total electron densities shows that the LC stabilizes the electrons around the long-range interaction regions of kinetic energy density, which are assumed to be electrons other than free electrons and self-interacting electrons, while the CCSD method stabilizes the electrons in the long-range interaction regions in the vertical molecular planes. As a more precise test, the LC effect on orbital densities are compared to the CCSD effect on Dyson orbital densities. Surprisingly, these effects are similar for the unoccupied orbitals, indicating that the LC covers the effects required to reproduce the CCSD Dyson unoccupied orbitals. For exploring the discrepancies between these effects on the occupied orbitals, the photoionization cross sections are calculated as a direct test for the shapes of the HOMOs to investigate the differences between these effects on the occupied orbitals. Consequently, the LC clearly produces the canonical HOMOs close to the CCSD Dyson and experimental ones, except for the HOMO of benzene molecule that mixes with the HOMO 1 for the CCSD Dyson orbitals. This indicates that the orbital analyses using the photoionization cross sections are available as a direct test for the quality of DFT functionals.
通过与从头算耦合簇单双激发（CCSD）方法的效果进行比较，研究了密度泛函理论（DFT）交换泛函的长程校正（LC）对分子总电子密度和轨道电子密度的影响。计算LC对总电子密度的影响表明，LC使动能密度的长程相互作用区域周围的电子稳定，这些电子被认为是除自由电子和自相互作用电子之外的电子，而CCSD方法使垂直分子平面内长程相互作用区域的电子稳定。作为更精确的测试，将LC对轨道密度的影响与CCSD对戴森轨道密度的影响进行比较。令人惊讶的是，对于未占据轨道，这些影响是相似的，这表明LC涵盖了重现CCSD戴森未占据轨道所需的影响。为了探究这些对占据轨道的影响之间的差异，计算了光电离截面，作为对最高占据分子轨道（HOMO）形状的直接测试，以研究这些对占据轨道的影响之间的差异。因此，除了苯分子的HOMO与CCSD戴森轨道的HOMO - 1混合外，LC明显产生了与CCSD戴森轨道和实验值接近的正则HOMO。这表明使用光电离截面进行的轨道分析可作为对DFT泛函质量的直接测试。
