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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.
Highlights
The recent success of computational chemistry in different areas of bio- and material sciences owes much to the development of density functional theory (DFT) methods [1] [2] allowing to study complex molecular systems containing many hundreds of atoms
A new density functional theory approach based on a complete active space self-consistent field (CASSCF) reference function in Extended Koopmans’ approximation is discussed
The number of generalizations of density functional theory based on a multiconfigurational CASSCF reference function with exact exchange (CASDFT) was introduced
Summary
The recent success of computational chemistry in different areas of bio- and material sciences owes much to the development of density functional theory (DFT) methods [1] [2] allowing to study complex molecular systems containing many hundreds of atoms. Despite many new modifications, there are still a number of difficulties in using DFT to properly describe some complex systems Such a situation arises as a result of a conflict between single-determinant, mean-field representation with the multiconfiguration nature of the strongly correlated molecular systems. To overcome these difficulties a number of solutions combining multiconfigurational wave function methods with DFT have been proposed This work presents a new approach and corresponding algorithm to avoid double counting problem by the decomposition of correlation energy into perturbation theory (PT) like series without introducing additional variables. The consistent theoretical argumentation of the developed approach is similar to [7] [9] and below we present the details of computational methodology that utilizes the Extended Koopmans’ approximation
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