Self-consistent linearized augmented-plane-wave study of the electronic structure and superconductivity of fcc lanthanum under pressure

We report the results of a linearized augmented-plane-wave calculation of the electronic structure of fcc La at three lattice constants corresponding to ambient pressure, 50, and 120 kbars. The Kohn-Sham-Gspar approximation for exchange and correlation is used and the potential is allowed a fully non-muffin-tin form. The f bands lie 2-2.5 eV above the Fermi level and are 1 eV wide, resulting in a very small (0.05 electrons) localized f occupation. Under pressure the f bands rise and broaden appreciably, resulting in only a slight increase in f occupation. The rigid-muffin-tin approximation for the electron-phonon interaction overestimates the superconducting transition temperature Tc by 40%, but we find that the drastic increase in Tc under pressure can be attributed primarily to changes in the electronic stiffness. Structural transitions which occur at 25 and 53 kbars may be related to changes in Fermi-surface topology which we find to occur approximately at these pressures.