An implementation of the density functional perturbation theory in the PAW framework

TL;DR

This paper presents an implementation of density functional perturbation theory within the PAW framework to compute linear susceptibilities, demonstrated through magnetic metal spectral functions, advancing ab initio material analysis.

Contribution

The paper introduces a novel implementation of density functional perturbation theory in the PAW framework for calculating linear susceptibilities and first-order wavefunctions.

Findings

Accurately computed magnon spectra for CrO₂ and Cu₂MnAl.

Identified small Landau damping in CrO₂ and significant damping in Cu₂MnAl.

Demonstrated agreement with experimental data for magnetic spectral functions.

Abstract

Quantifying materials' dynamical responses to external electromagnetic fields is central to understanding their physical properties. Here we present an implementation of the density functional perturbation theory for the computation of linear susceptibilities using the projector augmented-wave method. The Sternheimer equations are solved self-consistently through a nested iterative procedure to compute the first-order wavefunctions, from which the linear susceptibilities are obtained. As a demonstration, we compute the spin wave spectral functions of two magnetic metals. The computed magnon spectra for half-metallic CrO$_2$ and a Heusler intermetallic Cu$_2$MnAl show gapless Goldstone modes when spin rotation symmetry is preserved and display reasonable agreement with available experimental data. The Landau damping is computed to be small in CrO$_2$, but significant in Cu$_2$MnAl producing an asymmetric Lorentzian spectral lineshape. The access to linear susceptibilities as well as first-order wavefunctions offers a range of novel possibilities in quantitative understanding of materials' electronic properties from \textit{ab initio} methods.