Electronic structure of Millerite NiS

TL;DR

This study explores the electronic structure of millerite NiS using spectroscopic and computational methods, revealing the importance of electron correlations and covalency in its metallic behavior.

Contribution

It combines experimental spectroscopy with band structure and model Hamiltonian calculations to elucidate the electronic properties of millerite NiS, highlighting correlation effects.

Findings

Band structure describes valence spectra better than for hexagonal NiS

Electron correlation effects are significant even in metallic NiS

Millerite NiS is confirmed to be highly covalent pd-metal

Abstract

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