Projected Coupled Cluster Theory: Optimization of cluster amplitudes in the presence of symmetry projection

TL;DR

This paper introduces a method to optimize coupled cluster amplitudes in the presence of symmetry projection, enabling accurate description of both weak and strong electronic correlations with computational efficiency.

Contribution

It presents a novel approach for optimizing coupled cluster wave functions under symmetry projection, bridging weak and strong correlation treatments.

Findings

Effective optimization of cluster amplitudes with symmetry projection.

Application to Hubbard and molecular Hamiltonians.

Maintains computational scaling similar to traditional coupled cluster methods.

Abstract

Methods which aim at universal applicability must be able to describe both weak and strong electronic correlation with equal facility. Such methods are in short supply. The combination of symmetry projection for strong correlation and coupled cluster theory for weak correlation offers tantalizing promise to account for both on an equal footing. In order to do so, however, the coupled cluster portion of the wave function must be optimized in the presence of the symmetry projection. This paper discusses how this may be accomplished, and shows the importance of doing so for both the Hubbard model Hamiltonian and the molecular Hamiltonian, all with a computational scaling comparable to that of traditional coupled cluster theory.