The HSE hybrid functional within the FLAPW method and its application to GdN

TL;DR

This paper implements the HSE hybrid functional within the FLAPW method, enabling accurate electronic structure calculations, and applies it to GdN to clarify its ground-state properties and phase transition.

Contribution

The paper introduces a general approach to implement the HSE hybrid functional within the FLAPW method, improving accuracy in electronic structure calculations.

Findings

Accurate band gaps and lattice constants for semiconductors and insulators.

Identification of a half-metal to insulator transition in GdN.

Good agreement with experimental magnetic and electronic properties.

Abstract

We present an implementation of the Heyd-Scuseria-Ernzerhof (HSE) hybrid functional within the full-potential linearized augmented-plane-wave (FLAPW) method. Pivotal to the HSE functional is the screened electron-electron interaction, which we separate into the bare Coulomb interaction and the remainder, a slowly varying function in real space. Both terms give rise to exchange potentials, which sum up to the screened nonlocal exchange potential of HSE. We evaluate the former with the help of an auxiliary basis, defined in such a way that the bare Coulomb matrix becomes sparse. The latter is computed in reciprocal space, exploiting its fast convergence behavior in reciprocal space. This approach is general and can be applied to a whole class of screened hybrid functionals. We obtain excellent agreement of band gaps and lattice constants for prototypical semiconductors and insulators with electronic-structure calculations using plane-wave or Gaussian basis sets. We apply the HSE hybrid functional to examine the ground-state properties of rocksalt GdN, which have been controversially discussed in literature. Our results indicate that there is a half-metal to insulator transition occurring between the theoretically optimized lattice constant at 0 K and the experimental lattice constant at room temperature. Overall, we attain good agreement with experimental data for band transitions, magnetic moments, and the Curie temperature.