Connection between $GW$ and Extended Coupled Cluster
Abstract
Coupled-cluster (CC) theory and Green's function many-body perturbation theory (MBPT) have long evolved as distinct yet complementary frameworks for describing electronic correlation. While CC methods employ exponential wavefunction parametrizations that guarantee size extensivity and systematic improvability, Green's function approaches such as the approximation describe quasiparticle and optical excitations through diagrammatic resummations. Recent analyses have established a formal correspondence between these frameworks: the approximation is equivalent to an equation-of-motion (EOM) treatment of the direct-ring coupled-cluster doubles (drCCD) method. Within this context, the extended CC (ECC) ansatz offers a unified framework connecting CC and MBPT. This formulation bridges CC-based and Green's function-based methods, providing novel avenues for incorporating vertex corrections within a CC framework that keep a positive semi-definite self-energy and lead to potentially systematically improvable Green's function approaches.
Cite
@article{arxiv.2602.10887,
title = {Connection between $GW$ and Extended Coupled Cluster},
author = {Johannes Tölle and Marios-Petros Kitsaras and Andreas Irmler and Andreas Grüneis and Pierre-François Loos},
journal= {arXiv preprint arXiv:2602.10887},
year = {2026}
}