TITLE:
Extended Koopmans’ Approximation for CASDFT Exchange-Correlation Functional
AUTHORS:
Sergey Gusarov, Yurii Dmitriev
KEYWORDS:
DFT, CASSCF, CASDFT, Double Counting, Multiconfigurational
JOURNAL NAME:
Journal of Applied Mathematics and Physics,
Vol.6 No.6,
June
21,
2018
ABSTRACT:
A 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 P2(r) 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, P2(r)) and is based on Extended Koopmans’ theorem (EKT) approximation for
multiconfigurational wave function within CASSCF method.