Toward more accurate adiabatic connection approach for multireference wave functions

Abstract

A multiconfigurational adiabatic connection (AC) formalism is an attractive approach to computing dynamic correlation within CASSCF and 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 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 FCI 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 accuracy of the existing AC approximations.

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Cited by in corpus (3)

• Generalized many-body perturbation theory for the electron correlation energy: multi-reference random phase approximation via diagrammatic resummation
• Hilbert space multireference coupled clusters tailored by matrix product states
• Duality of particle-hole and particle-particle theories for strongly correlated electronic systems