Electron-phonon coupling in high-pressure Nb

The Fermi surface, phonon spectrum, and electron-phonon coupling parameter for metallic Nb under high pressure have been investigated with a full potential linearized augmented plane wave, linear muffin-tin orbital, and pseudopotential plane-wave methods. The results support the experimental observation of electronic topological transitions at 5 and 60 GPa. The lower pressure transition is related to a very subtle change in the topology of the Fermi surface as revealed in accurate calculations of the Hall coefficient. The transition at 60 GPa is identified with a change in the Fermi-surface topology due to the crossing of the electronic band along the $\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\Gamma}}N$ (\ensuremath{\Sigma}) direction in the cubic Brillouin zone. The calculated electron-phonon coupling parameters are in qualitative agreement with those derived from high-pressure experiment.