A local-density functional description of the valence transition in samarium sulphide

A self-consistent relativistic band-structure calculation on samarium sulphide using the local-densityapproximation is discussed.The LMTO method was used and the bands were calculated for several values of the lattice constant. The results of these calculations showthatalocal-densityfunctionalapproachcandescribethef-d valencetransition.The importance of using a fully relativistic treatment is emphasised.Inboth the high- and low- volume phases SmS shows a band-gap at the Fermi energy. The structural and bonding properties as they change through the transition are discussed in detail. Comparison with experimental measurements of the absorptive part of the dielectric function is made.