Effect of self-consistency and exchange on the electronic structure of the transition metals, V, Nb, and Ta

We have calculated densities of states, Fermi-surface areas, and effective masses from self-consistent augmented-plane wave band-structure calculations for the transition metals vanadium, niobium, and tantalum using the Xα exchange approximation. Our results are compared in detail both with the experimental results and the earlier self-consistent and non-self-consistent calculations using other commonly used exchange approximations. We find that the calculated Fermi surfaces are quite sensitive to the exchange approximation used, especially for vanadium. For the self-consistent calculations, there is better overall agreement with the experimental results for the α=2/3 than for the Xα calculations. Certain detailed aspects of the experimental Fermi-surface results are discussed and interpreted using the present calculations. We find considerable anisotropy in the electron-phonon mass-enhancement factor obtained from the Fermi-surface results. This anisotropy is found to be very sensitive to the different exchange approximations and to self-consistency.