Toward more accurate adiabatic connection approach for multireference wavefunctions

Matoušek, Mikuláš; Hapka, Michał; Veis, Libor; Pernal, Katarzyna

doi:10.1063/5.0131448

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Toward more accurate adiabatic connection approach for multireference wavefunctions

Matoušek, Mikuláš·Hapka, Michał·Veis, Libor·Pernal, Katarzyna

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Abstract

A multiconfigurational adiabatic connection (AC) formalism is an attractive approach to compute the dynamic correlation within the complete active space self-consistent field and density matrix renormalization group (DMRG) models. Practical realizations of AC have been based on two approximations: (i) fixing one- and two-electron reduced density matrices (1- and 2-RDMs) at the zero-coupling constant limit and (ii) extended random phase approximation (ERPA). This work investigates the effect of removing the “fixed-RDM” approximation in AC. The analysis is carried out for two electronic Hamiltonian partitionings: the group product function- and the Dyall Hamiltonians. Exact reference AC integrands are generated from the DMRG full configuration interaction solver. Two AC models are investigated, employing either exact 1- and 2-RDMs or their second-order expansions in the coupling constant in the ERPA equations. Calculations for model molecules indicate that lifting the fixed-RDM approximation is a viable way toward improving the accuracy of existing AC approximations.

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Matoušek, Mikuláš, Hapka, Michał, Veis, Libor, Pernal, Katarzyna. 2023-02-02. Toward more accurate adiabatic connection approach for multireference wavefunctions. https://doi.org/10.1063/5.0131448

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