Implementation of the density functional perturbation theory for generalized susceptibility in the projector augmented wave framework
Xiaoqiang Liu, Yihao Lin, Ji Feng
Abstract
The quantification of 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 wave functions, 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 ${\mathrm{CrO}}_{2}$ and a Heusler intermetallic ${\mathrm{Cu}}_{2}\mathrm{MnAl}$ 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 ${\mathrm{CrO}}_{2}$, but significant in ${\mathrm{Cu}}_{2}\mathrm{MnAl}$, producing an asymmetric Lorentzian spectral line shape. The access to linear susceptibilities as well as first-order wave functions offers a range of novel possibilities in the quantitative understanding of materials' electronic properties from ab initio methods.