Electronic structure of 3d pyrite- and marcasite-type sulphides

Electronic structure calculations are reported for the 3d pyrite-type sulphides Fes 2 , CoS 2 , NiS 2 , CuS 2 and ZnS 2 , and for marcasite-type FeS 2 . The energy bands are compared with the experimental data available. FeS 2 is calculated to be a semiconductor, with an indirect gap of 0.7 eV (pyrite) or 0.4 eV (marcasite) separating filled t 2g and empty e g sub-bands. In ZnS 2 the d band falls below the main, fully occupied S p bands to give a semiconducting gap approximately=2 eV to the lowest metal s and S 2 p sigma * bands. The intermediate compounds CoS 2 , NiS 2 and CuS 2 , within the present limitations of delocalised electrons and paramagnetic exchange potentials, are found to be metals; in these the d states move steadily down through the S p bands. Sulphur s and p valence bands extend through energy ranges 11-19 eV and 2-9 eV respectively below the Fermi level, in good agreement with photoelectron spectra.