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.