CALCULATED ELECTRONIC-STRUCTURE OF THE SANDWICH D(1) METALS LAI2 AND CEI2 - APPLICATION OF NEW LMTO TECHNIQUES

The electronic structures of the cubic layered d(1) metals LaI2 and Ce I2 were calculated using local density-functional theory and the linea r muffin-tin orbital method. Special care was taken in the sphere pack ing used for the atomic spheres approximation. The band structure and the bonding were analysed in terms of projections of the bands onto or thogonal orbitals. The conduction-band structure could be calculated w ith a down-folded two-orbital basis which then served for the construc tion of an analytical 2 x 2 orthogonal, two-center tight-binding Hamil tonian. The conduction band has almost pure Ln-Ln 5d e(g) character. T he x(2) - y(2) contribution dominates and is two-dimensional and short ranged. Strong hybridization with the 3z(2) - 1 orbital occurs near t he saddle point, which is thereby lowered in energy and bifurcated due to the k(z)-dispersion provided by the 3z(2) - 1 orbital. This streng thens the metal-metal bonds and prevents the nesting instability of th e Fermi surface of the half filled x(2) - y(2) band. Within the limite d accuracy of the LDA, the band structure of CeI2 was found to be iden tical to that of LaI2. The conduction-band 4f hybridization V-df(2) (0 ) was analysed and found to be several times smaller than in fee gamma -Ce, in qualitative agreement with recent photoemission results [1]. O f importance for this reduction seems to be that the conduction band i s formed by essentially only one orbital, Ce 5d(x2-y2), that the numbe r of Ce nearest-neighbors is small, and that the Ce-Ce distance is rel atively large.