Ab Initio Lifetime and Concomitant Double-Excitation Character of Plasmons at Metallic Densities

TL;DR

This paper uses advanced coupled-cluster theory to accurately compute plasmon properties in the uniform electron gas, revealing a many-state resonance with significant double-excitation character, advancing understanding of plasmon lifetimes.

Contribution

It demonstrates that EOM-CCSD predicts a multi-state plasmon resonance with high double-excitation character, providing an ab initio approach to plasmon linewidths in condensed matter.

Findings

EOM-CCSD predicts a many-state plasmon resonance.

Each state has over 80% double-excitation character.

Results agree with previous diagrammatic calculations.

Abstract

The accurate calculation of excited state properties of interacting electrons in the condensed phase is an immense challenge in computational physics. Here, we use state-of-the-art equation-of-motion coupled-cluster theory with single and double excitations (EOM-CCSD) to calculate the dynamic structure factor, which can be experimentally measured by inelastic x-ray and electron scattering. Our calculations are performed on the uniform electron gas at densities corresponding to Wigner-Seitz radii of $r_s=5$, 4, and 3 corresponding to the valence electron densities of common metals. We compare our results to those obtained using the random-phase approximation, which is known to provide a reasonable description of the collective plasmon excitation and which resums only a small subset of the polarizability diagrams included in EOM-CCSD. We find that EOM-CCSD, instead of providing a perturbative improvement on the RPA plasmon, predicts a many-state plasmon resonance, where each contributing state has a double-excitation character of 80\% or more. This finding amounts to an ab initio treatment of the plasmon linewidth, which is in good quantitative agreement with previous diagrammatic calculations, and highlights the strongly correlated nature of lifetime effects in condensed-phase electronic structure theory.