Electronic structure of GdN, and the influence of exact exchange

TL;DR

This study compares electronic structures of GdN using local density approximation, Hartree-Fock, and hybrid functional B3LYP, revealing differences in metallic and insulating behaviors and the impact of exact exchange.

Contribution

It demonstrates the capability of the CRYSTAL06 code to treat GdN with explicit 4f electrons and explores multiple solutions at the B3LYP level.

Findings

LDA predicts half-metallic behavior

Hartree-Fock predicts an insulating gap

B3LYP yields multiple solutions with varying electronic properties

Abstract

GdN bulk is studied with the local density approximation, on the Hartree-Fock level, and on the level of the hybrid functional B3LYP. A local basis set formalism is used, as implemented in the present CRYSTAL06 release. It is demonstrated that the code is technically capable of treating this system with its 4f electrons explicitly, i.e. out of the core. The band structure at the level of the local density approximation is in good agreement with earlier calculations and is found to be half-metallic. The Hartree-Fock band structure is insulating with a large gap. Interestingly, three solutions were found at the B3LYP level. The lowest of them is insulating for majority spin, and the Fermi surface for minority spin consists only of points, resulting in a very low density of states around the Fermi level.