First-principles study of phonons and superconductivity of Nb1−xMox within the virtual-crystal approximation

We have studied the complete phonon dispersion, electron-phonon and superconducting properties of the Nb1-xMox alloy within the framework of density functional perturbation theory using a mixed-basis pseudopotential method and the self-consistent virtual-crystal approximation. Complete phonon dispersions as a function of x were obtained in good agreement with experimental data, independent of the approximation used for the exchange-correlation functional. For the Eliashberg function alpha2F(omega) we found a shift of weight to higher frequencies as well as an overall reduction with increasing x up to x0.7; however, for x = 1 (pure Mo) the spectral weight for alpha2F(omega) increased again. We used the information of alpha2F(omega) to calculate and analyze the evolution of the average coupling strength lambda(x) and the superconducting temperature Tc(x). The variation of lambda(x) closely follows the variation of the electronic density of states at EF. For Tc(x) experimental values were well reproduced provided a proper interpolation scheme for the Coulomb pseudopotential mu*(x) was employed.