Structural, electronic and magnetic properties of greigite FeSby GGA and GGA+versus SCAN meta-GGA density functionals.

The performance of exchange-correlation functional of density functional theory represented in generalized gradient approximation (GGA) and in the strongly constrained and appropriately normed (SCAN) meta-GGA scheme to study structural, electronic, and magnetic properties of greigite (FeS) was investigated. The effects of inclusion of strong electron correlations represented by on-site Hubbard correction, and nonlocality of the long-range van der Waals (vdW) interactions were also considered. Geometry optimization yielded the inverse spinel structure and lattice parameter of greigite in good agreement with experimental data. Calculated electronic structure revealed a half-metallic nature of the greigite bands for the applied functionals except for GGA, which predicts metallic behavior. Antiferromagnetic coupling of iron ions in tetrahedral and octahedral coordinations makes the overall crystal structure ferrimagnetic. In general the GGA+and SCAN show comparable performance in prediction physical properties of greigite. Inclusion of the vdW correction does not change the character of the bands.