Calculated electronic structure of the sandwichd ¹ metals LaI₂ and CeI₂: Application of new LMTO techniques

Abstract

The electronic structures of the cubic layeredd ¹ metals LaI₂ and CeI₂ were calculated using local density-functional theory and the linear muffin-tin orbital method. Special care was taken in the sphere packing used for the atomic spheres approximation. the band structure and the bonding were analysed in terms of projections of the bands onto orthogonal orbitals. The conduction-band structure could be calculated with a down-folded two-orbital basis which then served for the construction of an analytical 2×2 orthogonal, two-center tight-binding Hamiltonian. The conduction band has almost pure Ln-Ln 5d e _g character. Thex ²−y ²contribution dominates and is two-dimensional and short ranged. Strong hybridization with the 3z ²−1 orbital occurs near the saddle point, which is thereby lowered in energy and bifurcated due to thek _z -dispersion provided by the 3z ²−1 orbital. This strengthens the metal-metal bonds and prevents the nesting instability of the Fermi surface of the half filledx ²−y ²band. Within the limited accuracy of the LDA, the band structure of CeI₂ was found to be identical to that of LaI₂. The conduction-band 4f hybridizationV ² _{d f} (0) was analysed and found to be several times smaller than in fcc γ-Ce, in qualitative agreement with recent photoemission results [1]. Of importance for this reduction seems to be that the conduction band is formed by essentially only one orbital,$Ce 5d_{x^2 - y^2 }$,that the number of Ce nearest-neighbors is small, and that the Ce−Ce distance is relatively large.