Phonons from Density-Functional Perturbation Theory using the All-Electron Full-Potential Linearized Augmented Plane-Wave Method FLEUR

TL;DR

This paper presents a novel implementation of phonon calculations using density-functional perturbation theory within the all-electron full-potential linearized augmented plane-wave method in the FLEUR software, validated against other methods and experiments.

Contribution

It introduces a new all-electron, full-potential DFPT implementation for phonons in the FLEUR code, handling the complexities of the LAPW basis and muffin-tin spheres.

Findings

Accurate phonon dispersions for various solids including metals and insulators.

Excellent agreement with finite displacement methods and experimental data.

Validated the implementation across different material types.

Abstract

Phonons are quantized vibrations of a crystal lattice that play a crucial role in understanding many properties of solids. Density functional theory (DFT) provides a state-of-the-art computational approach to lattice vibrations from first-principles. We present a successful software implementation for calculating phonons in the harmonic approximation, employing density-functional perturbation theory (DFPT) within the framework of the full-potential linearized augmented plane-wave (FLAPW) method as implemented in the electronic structure package FLEUR. The implementation, which involves the Sternheimer equation for the linear response of the wave function, charge density, and potential with respect to infinitesimal atomic displacements, as well as the setup of the dynamical matrix, is presented and the specifics due to the muffin-tin sphere centered LAPW basis-set and the all-electron nature are discussed. As a test, we calculate the phonon dispersion of several solids including an insulator, a semiconductor as well as several metals. The latter are comprised of magnetic, simple, and transition metals. The results are validated on the basis of phonon dispersions calculated using the finite displacement approach in conjunction with the FLEUR code and the phonopy package, as well as by some experimental results. An excellent agreement is obtained.