Gould Tim, Hashimi Zahed, Kronik Leeor, Dale Stephen G
Queensland Micro- and Nanotechnology Centre, Griffith University, Nathan, QLD 4111, Australia.
Department of Molecular Chemistry and Materials Science, Weizmann Institute of Science, Rehovoth 76100, Israel.
J Phys Chem Lett. 2022 Mar 17;13(10):2452-2458. doi: 10.1021/acs.jpclett.2c00042. Epub 2022 Mar 10.
In calculations based on density functional theory, the "HOMO-LUMO gap" (difference between the highest occupied and lowest unoccupied molecular orbital energies) is often used as a low-cost, ad hoc approximation for the lowest excitation energy. Here we show that a simple correction based on rigorous ensemble density functional theory makes the HOMO-LUMO gap exact in principle and significantly more accurate in practice. The introduced perturbative ensemble density functional theory approach predicts different and useful values for singlet-singlet and singlet-triplet excitations, using semilocal and hybrid approximations. Excitation energies are similar in quality to time-dependent density functional theory, especially at high fractions of exact exchange. The approach therefore offers an easy-to-implement and low-cost route to robust prediction of molecular excitation energies.
在基于密度泛函理论的计算中，“最高已占分子轨道与最低未占分子轨道能量之差”（HOMO-LUMO能隙）常被用作最低激发能的低成本临时近似。在此我们表明，基于严格的系综密度泛函理论的一种简单校正使得HOMO-LUMO能隙在原则上精确，在实际中显著更准确。引入的微扰系综密度泛函理论方法使用半局域和杂化近似来预测单重态-单重态和单重态-三重态激发的不同且有用的值。激发能在质量上与含时密度泛函理论相似，特别是在精确交换的高比例时。因此，该方法为分子激发能的可靠预测提供了一条易于实施且低成本的途径。
