Recent Development of Multireference Density Functional Theory

Abstract

We review a recently developed ab initio multireference (MR)-density functional theory (DFT) approach based on the partially interacting reference systems. Instead of Kohn–Sham equations, we introduce the auxiliary CI equation with the effective DFT potential field. For practice, we classify electrons of the target system into valence electrons and other electrons. The former plays the quantum resonating feature of electronic structure of molecular species, while the latter affects the electronic properties via the effective correlation potential for the former electrons. The theoretical devices in our MR-DFT are introduced to avoid the double counting problem for any combination of a wavefunction and a correlation functional. Some numerical examples are presented.

Theory and computations of two-photon absorbing photochromic chromophores

“…There are several extensions of DFT, developed to describe the excited states. One approach is to use multireference strategies [36][37][38][39]. More often, however, DFT is combined with the time dependent perturbation theory approach, which we shall briefly review next.…”

Local-spin-density functional for multideterminant density functional theory

“…Refs. 6,7,8,9,10,11,12,13,14,15,16,17,18). The idea is to use different approximations for the LR and the SR contributions to the exchange and/or correlation energy density functionals of the Kohn-Sham (KS) scheme.…”

Spin‐optimized resonating Hartree‐Fock configuration interaction

“…For such cases, the “resonating” type of electron correlations is beyond the scope of the Kohn‐Sham (KS) density functional theory (DFT) 5, because the KS‐DFT is based on the noninteracting reference system. Recently, many researchers not only in the field of quantum chemistry 6–9 but also in the field of condensed matter physics 10–12 have come to recognize the importance of multireference effects in the strongly correlated electron systems. For small molecular systems, both of near‐degeneracy effects and the higher‐order electron correlation effects are treated with the straightforward complete‐active‐space based perturbation (CASPT) or configuration interaction (MRCI) method.…”