Electronic structure and Fermi surfaces of the superconductive A3B compounds: A = V, Nb; B = Ga, Ge and Sn

The full-potential linearized augmented-plane wave (FP-LAPW) method is employed in calculations of the band structure and Fermi surfaces of the superconductive A15 (Cr3O-type) compounds V 3B and Nb3B, B=Ga, Ge and Sn. A plot of the total density of states shows a minimum above E F  in all studied compounds separating bonding bands from antibonding bands. The V compounds possess higher densities of states at E F , whereas narrower bandwidths are observed for the Nb compounds. From the results it is inferred that the higher transition temperature T c  experimentally observed for the Nb compounds arises from larger volumes of the Fermi surfaces for electron sheets besides the multi-Fermi-surface structure.