New approach for multiconfigurational Exchange-Correlation Functional

TL;DR

This paper introduces a new density functional theory approach based on CASSCF and Extended Koopmans' approximation, avoiding complex reparametrizations and additional variables for multiconfigurational systems.

Contribution

It proposes a novel multiconfigurational exchange-correlation functional that simplifies calculations by eliminating the need for on-top pair density variables.

Findings

The new approach is computationally less demanding.

It maintains accuracy without reparametrizing existing functionals.

It extends DFT applicability to multiconfigurational systems.

Abstract

New density functional theory approach based on a complete active space self-consistent field (CASSCF) reference function in Extended Koopmans' approximation is discussed. Recently, the number of generalizations of density functional theory based on a multiconfigurational CASSCF reference function with exact exchange (CASDFT) was introduced. It was shown by one of the authors (Dr. Gusarov) that such a theory could be formulated by introducing a special form of exchange-correlation potential. To take into account an active space and to avoid double counting of correlation energy the dependence from on-top pair density as a new variable was introduced. Unfortunately, this requires a deep review and reparametrization of existing functional expressions which lead to additional computational difficulties. The presented approach does not require introducing additional variables (like on-top pair density, and based on Extended Koopmans' theorem (EKT) approximation for multiconfigurational wave function within CASSCF method.