Band structure for some Nb₃X compounds

The tight binding method is used to calculate band structure for a number of Nb₃X compounds. The 4d band of the niobium, as well as the s-p bands of the X-atoms, are considered. The transfer and overlap integrals are calculated using tabulated atomic orbitals. The crystal field parameters (CFP) are estimated more carefully, taking into account deviations from a muffin-tin potential. We employ here the independent band approximation in which no interband interaction is considered. This approximation has been proved successful for the V₃Ga case, and it is estimated here that interband interaction may shift some levels up or down by 50 mRy or so, but the overall band-structure does not change. The Fermi level is found to lie in the neighbourhood of three peaks; one belongs to the δ₂(d_xy) band and the two others belong to the π(d_xz, d_yz) band.