Empirical LSDA+U study for electronic structure of hexagonal NiS

Electronic-structure calculations have been carried out for hexagonal NiS w ith the use of the full-potential linearized augmented plane-wave (FLAPW) m ethod in the local-spin-density approximation +U (LSDA + U) approach. The U parameter is treated as an empirical parameter to improve the band structu re near the Fermi energy. It is found that this approach succeeds in obtain ing the antiferromagnetic state which is the ground state of NiS, and the i nsulating stale with an energy gap of similar to 0.1eV. The photoemission s pectra obtained from the density of slates of the LSDA+U, however, fail to explain experiment. We conclude that further advanced treatment of electron -electron interaction is needed for describing the single-electron excited state of hexagonal NiS.