Electron energy loss spectroscopy of bulk gold with ultrasoft pseudopotentials and the Liouville-Lanczos method

TL;DR

This paper introduces a new computational approach combining ultrasoft pseudopotentials with the Liouville-Lanczos method to analyze electron energy loss spectra in bulk gold, revealing detailed electronic excitation features.

Contribution

The study extends time-dependent density-functional perturbation theory with ultrasoft pseudopotentials and applies the Liouville-Lanczos method to bulk gold, uncovering distinct 5d and 6s electron gas oscillations.

Findings

Identification of separate 5d and 6s electron gases in gold.

Detection of a mixed excitation near 2.2 eV involving interband transitions.

Calculation of the EEL spectrum at various momentum transfers.

Abstract

The implementation of ultrasoft pseudopotentials into time-dependent density-functional perturbation theory is detailed for both the Sternheimer approach and the Liouville-Lanczos (LL) method, and equations are presented in the scalar relativistic approximation for periodic solids with finite momentum transfer q. The LL method is applied to calculations of the electron energy loss (EEL) spectrum of face-centered cubic bulk Au both at vanishing and finite q. Our study reveals the richness of the physics underlying the various contributions to the density fluctuation in gold. In particular, our calculations suggest the existence in gold of two quasi-separate 5d and 6s electron gasses, each one oscillating with its own frequency at resp. 5.1 eV and 10.2 eV. We find that the contribution near 2.2 eV comes from 5d to 6s interband transitions modified by the intraband contribution to the real part of the dielectric function, which we call a mixed excitation.