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

Abstract

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-Gáspar 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 $\lambda$ overestimates the superconducting transition temperature $T_c$ by 40%, but we find that the drastic increase in $T_c$ under pressure can be attributed primarily to changes in the electronic stiffness $\eta$. 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.