First-principles study of the electronic structure of NiS, NiS$_{2}$, and Ni$_{3}$S$_{2}$

First-principles study of the electronic structure of NiS, NiS$_{2}$, and Ni$_{3}$S$_{2}$ are performed. DFT+U and HSE hybrid functional are used as the primary exchange-correlation schemes. The resulting electronic structures at various phases are analyzed, and the results compared with previous experimental and theoretical work.