Electronic structure of millerite NiS

We investigate the electronic structure of Nickel sulphide (NiS) in the\nmillerite phase using electron spectroscopic measurements and band structure as\nwell as model Hamiltonian calculations. While band structure calculations are\nfound to be relatively more successful in describing the experimental valence\nband spectrum of this highly conducting phase compared to the hexagonal phase\nof NiS, cluster calculations including electron correlation effects are found\nto be necessary for the description of certain features in the experimental\nspectra, indicating importance of correlation effects even in a highly metallic\nsystem. The electronic parameter strengths obtained from these calculations\nconfirm that the millerite NiS is a highly covalent pd-metal. The comparative\nstudy of hexagonal and millerite forms of NiS, provides the information\nconcerning the evolution of the spectral function in a pd-metal as a function\nof covalency.\n