Constructing `full-frequency' spectra via moment constraints for coupled cluster Green's functions

TL;DR

This paper introduces a method to construct full-frequency quasiparticle spectra using moment constraints derived from coupled-cluster calculations, enabling efficient and accurate spectral representations across all energy scales.

Contribution

The authors develop a systematic approach to generate full-frequency spectra from static expectation values computed at the coupled-cluster level, improving efficiency and accuracy.

Findings

Converges excitation spectra within CCSD accuracy.

Requires less computational effort than traditional Green's function methods.

Provides complete spectral information at all energy scales.

Abstract

We propose an approach to build `full-frequency' quasiparticle spectra from conservation of a set of static expectation values. These expectation values define the moments of the spectral distribution, resulting in an efficient and systematically improvable expansion. By computing these initial moment constraints at the coupled-cluster level, we demonstrate convergence in both correlated state-specific and full spectral quantities, while requiring a fraction of the effort of traditional Green's function approaches. Tested across the GW100 benchmark set for charged excitation spectra, we can converge frontier excitations to within the inherent accuracy of the CCSD approximation, whilst obtaining a simultaneous representation of the entire excitation spectrum at all energy scales.