Capturing Static and Dynamic Correlation with ΔNO-MP2 and ΔNO-CCSD

28 August 2019, Version 1
This content is a preprint and has not undergone peer review at the time of posting.

Abstract

The NO method for static correlation is combined with second-order Mller-Plesset perturbation theory (MP2) and coupled-cluster singles and doubles (CCSD) to account for dynamic correlation. The MP2 and CCSD expressions are adapted from nite-temperature CCSD, which includes orbital occupancies and vacancies, and expanded orbital summations. Correlation is partitioned with the aid of damping factors incorporated into the MP2 and CCSD residual equations. Potential energy curves for a selection of diatomics are in good agreement with extrapolated full conguration interaction results (exFCI), and on par with conventional multireference approaches.

Keywords

static correlation
dynamic correlation
strongly correlated systems
strong correlation
coupled cluster
perturbation theory
finite temperature formalism
natural orbital functional theory
natural orbitals
correlation energy

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