X-ray photoemission study of NiS<SUB>2&#8722;x</SUB>Se<SUB>x</SUB> (x=0.0-1.2)

Electronic structure of NiS<SUB>2&#8722;x</SUB>Se<SUB>x</SUB> system has been investigated for various compositions (x) using x-ray photoemission spectroscopy. An analysis of the core-level as well as the valence-band spectra of NiS<SUB>2</SUB>in conjunction with many-body cluster calculations provides a quantitative description of the electronic structure of this compound. With increasing Se content, the on-site Coulomb correlation strength (U) does not change, while the bandwidth W of the system increases, driving the system from a covalent insulating state to a pd-metallic state