Valence ππ* Excitations in Benzene Studied by Multiconfiguration Pair-Density Functional Theory

We explore the valence singlet and triplet ππ* excitations of benzene with complete active pace self-consistent field (CASSCF) theory, complete active space perturbation theory (CASPT2), and multiconfiguration pair-density functional theory (MC-PDFT) for four different choices of active space. We propose a new way to quantify the covalent and ionic character of the electronic states in terms of the components of the total electronic energy. We also explore the effect of scaling the exchange and correlation components of the on-top density functional used in MC-PDFT; we observe that increasing the exchange contribution improves the MC-PDFT excitation energies for benzene.

我们针对苯的价态单重态与三重态ππ*激发态，结合四种不同的活性空间选取方案，采用完全活性空间自洽场（complete active space self-consistent field, CASSCF）理论、完全活性空间微扰理论（complete active space perturbation theory, CASPT2）与多组态对密度泛函理论（multiconfiguration pair-density functional theory, MC-PDFT）开展研究。我们提出了一种全新方法，可基于总电子能量的组分量化电子态的共价性与离子性特征。我们还考察了MC-PDFT中所用上位密度泛函的交换与关联分量的缩放效应；研究发现，提升交换分量占比可改善苯的MC-PDFT激发能计算结果。