Modified $GW$ Method in Electronic Systems

TL;DR

This paper introduces a modified GW approximation that improves accuracy in strongly correlated electronic systems while maintaining similar computational costs, validated against exact and numerical methods.

Contribution

A novel GW-based method with a different truncation scheme and covariant formulation, enhancing accuracy in strong-coupling regimes compared to existing approaches.

Findings

More precise Green's function in strong-coupling regimes

Excellent agreement of charge correlator with DQMC results

Comparable computational complexity to traditional GW method

Abstract

A modified $GW$ approximation to many - body systems is developed. The approximation has the same computational complexity as the traditional $GW$ approach, but uses a different truncation scheme. This scheme neglects high order connected correlation functions. A covariant (preserving Ward identities due to charge conservation) scheme for two - body correlators is employed, which holds the relation between the charge correlator and charge susceptibility. The method is tested on the two - dimensional one - band Hubbard model. Results are compared with exact diagonalization, the fluctuation - exchange (FLEX) theory and determinantal quantum Monte Carlo (DQMC) approach. The comparison for the (one - body) Green's function demonstrates that it is more precise in strong - coupling regime (especially away from half - filling) than similar - complexity approximations $GW$ or FLEX. The charge correlator is in excellent agreement with the numerically exact result obtained from DQMC.