Symmetry conserving Coupled Cluster Doubles wave function and the Self-Consistent odd particle number RPA

TL;DR

This paper introduces a symmetry-conserving Coupled Cluster Doubles wave function combined with a self-consistent odd particle number RPA, leading to accurate ground state energies and occupation numbers across various interaction strengths.

Contribution

It develops a novel symmetry-conserving CCD wave function and integrates it with a self-consistent odd-RPA approach, improving the description of correlation effects.

Findings

Accurate ground state energies in an exactly solvable model.

Self-consistent single particle occupation numbers.

Effective handling of correlations from weak to strong couplings.

Abstract

Mixing single and triple fermions an exact killing operator of the Coupled Cluster Doubles (CCD) wave function with good symmetry was found in \cite{Tohy13}. Using these operators with the equation of motion (EOM) method the so-called self-consistent odd particle number random phase approximation (odd-RPA) was set up. Together with the stationarity condition of the two body density matrix it is shown that the killing conditions allow to reduce the order of correlation functions contained in the matrix elements of the odd-RPA equations to a fully self consistent equation for the single particle occupation numbers. Excellent results for the latter and the ground state energies are obtained in an exactly solvable model from weak to strong couplings.