The GW plus cumulant method and plasmonic polarons: application to the homogeneous electron gas

TL;DR

This paper compares the GW and GW plus cumulant methods for calculating the spectral function of the homogeneous electron gas, showing how the cumulant approach reduces spurious features and reveals plasmonic polaron bands.

Contribution

It applies the GW plus cumulant method to the homogeneous electron gas, demonstrating improved spectral features and the emergence of plasmonic polaron bands.

Findings

GW spectral function shows a spurious plasmaron peak.

GW plus cumulant reduces plasmonic feature intensity.

Identification of plasmonic polaron bands in HEG.

Abstract

We study the spectral function of the homogeneous electron gas using many-body perturbation theory and the cumulant expansion. We compute the angle-resolved spectral function based on the GW approximation and the `GW plus cumulant' approach. In agreement with previous studies, the GW spectral function exhibits a spurious plasmaron peak at energies 1.5$\omega_{\rm pl}$ below the quasiparticle peak, $\omega_{\rm pl}$ being the plasma energy. The GW plus cumulant approach, on the other hand, reduces significantly the intensity of the plasmon-induced spectral features and renormalizes their energy relative to the quasiparticle energy to $\omega_{\rm pl}$. Consistently with previous work on semiconductors, our results show that the HEG is characterized by the emergence of plasmonic polaron bands, that is, broadened replica of the quasiparticle bands, red-shifted by the plasmon energy.