Electronic structure, superconductivity, and spin fluctuations in the $A15\mathrm{}$ compounds $A_{3}B$: $A=V$, Nb; $B=\mathrm{I}\mathrm{r},\mathrm{P}\mathrm{t},\mathrm{A}\mathrm{u}$

The electronic structure of six $A15\mathrm{}$ compounds ${\mathrm{V}}_3$Ir, ${\mathrm{V}}_3$Pt, ${\mathrm{V}}_3$Au, ${\mathrm{Nb}}_3$Ir, ${\mathrm{Nb}}_3$Pt, and ${\mathrm{Nb}}_3$Au has been determined by means of self-consistent semirelativistic linear muffin-tin orbital band calculations. Parameters related to superconductivity such as electron-phonon coupling, transition temperature, electronic specific heat, and magnetic exchange enhancement are derived from the electronic-structure results. Generally the results obtained agree well with experimental values, with the exception of ${\mathrm{Nb}}_3$Pt and ${\mathrm{V}}_3$Au. In the former compound the density of states (DOS) has a sharp increase at $E_F$ making the exact DOS value uncertain. In ${\mathrm{V}}_3$Au the high calculated $T_c$ and the Stoner factor indicate that spin fluctuations may be limiting the $T_c$.