Capturing static and dynamic correlation with $\Delta \text{NO}$-MP2 and $\Delta \text{NO}$-CCSD

TL;DR

This paper introduces a combined static and dynamic correlation method using $ ext{NO}$-based approaches with MP2 and CCSD, achieving accurate potential energy curves comparable to full configuration interaction results.

Contribution

The authors develop a novel approach integrating $ ext{NO}$-based static correlation with MP2 and CCSD for dynamic correlation, adapted from finite-temperature CCSD.

Findings

Potential energy curves agree well with exFCI results

Method performs on par with traditional multireference approaches

Effective partitioning of correlation using damping factors

Abstract

The $\Delta \text{NO}$ method for static correlation is combined with second-order M{\o}ller-Plesset perturbation theory (MP2) and coupled-cluster singles and doubles (CCSD) to account for dynamic correlation. The MP2 and CCSD expressions are adapted from finite-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 configuration interaction results (exFCI), and on par with conventional multireference approaches.