Real-time coupled-cluster approach for the cumulant Green's function

TL;DR

This paper introduces a non-perturbative, coupled-cluster based cumulant Green's function method that improves the accuracy of electronic excitation properties and spectral features in molecular systems.

Contribution

It develops a non-linear, coupled-cluster approach to the cumulant Green's function, extending previous linear methods for better accuracy in excited state calculations.

Findings

Significant improvements in core-level binding energies.

Enhanced modeling of inelastic loss satellites.

Non-linear corrections improve quasiparticle descriptions.

Abstract

Green's function methods within many-body perturbation theory provide a general framework for treating electronic correlations in excited states. Here we investigate the cumulant form of the one-electron Green's function based on the coupled-cluster equation of motion approach in an extension of our previous study. The approach yields a non-perturbative expression for the cumulant in terms of the solution to a set of coupled first order, non-linear differential equations. The method thereby adds non-linear corrections to traditional cumulant methods linear in the self energy. The approach is applied to the core-hole Green's function and illustrated for a number of small molecular systems. For these systems we find that the non-linear contributions lead to significant improvements both for quasiparticle properties such as core-level binding energies, as well as the satellites corresponding to inelastic losses observed in photoemission spectra.