Systematics for trivalent and divalent rare-earth sulphides

The electronic structures of the rare-earth monosulphides are calculated wi th the self-interaction corrected local-spin-density approximation. This sc heme allows part of the rare-earth f shell to be localized. Both trivalent and divalent configurations of the rare earths are considered, and the syst ematics in lattice constants and electronic densities of states are investi gated. The scheme is found to be accurate in describing the properties of t hese systems and reveals that two kinds of f electrons in fact are present in the rare-earth monosulphides, namely both localized atomic-like f electr ons and itinerant band f electrons, which hybridize with the normal conduct ion bands. The stability of the divalent configuration directly correlates with the number of band f electrons.