Electronic structure and thermodynamic properties of millerite NiS from first principles: Complex fermi surface and large thermal expansion coefficient

The electronic structure, Fermi surface, phonon dispersion, and thermodynamic properties of millerite nickel sulfide (NiS) have been investigated systemically from first principles. The calculations suggest that there are two bands across the Fermi level, and the corresponding Fermi surfaces are very complex, which implies the rich physical and chemical properties of this material. The predicted phonon frequencies of millerite are in good agreement with recent Raman spectroscopy experiment. In addition, the temperature-dependent equilibrium volumes, bulk moduli, and thermodynamic properties including heat capacities, entropies and thermal expansion coefficient are also determined by quasi harmonic approximation (QHA), which are found to agree with available experiment. Most importantly, we also found that the predicted thermal expansion coefficients of millerite NiS are larger than glass. This suggested that thermal expansion may contribute an additional enhancement to the volume expansion induced by α-β phase transformation of NiS and thus increase the risks of the spontaneous failure of thermally toughened glass. The various properties present here will be useful for understanding the underlying mechanism of performance degradation and failure related to NiS under working conditions.