High-pressure band structure and superconductivity of bcc and fcc lithium

The electronic band structure, density of states, Fermi surface cross sections and superconductivity of bcc and fcc lithium (Li) as a function of pressure are investigated. The high-pressure band structure exhibits significant deviations from the normal-pressure band structure due to s-->p transition. At normal pressure, the superconducting transition of bcc-Li occurs at 0.12 mK. On further increase of pressure, T-c increases considerably and its maximum value may exceed 40 K (at 1.65 Mbar) both in bcc and fcc lithium. At 0.48 Mbar pressure, the calculated value of T-c is very close to the experimental value of 20 K. The high-pressure bcc and fcc lithium Fermi surfaces are distorted spheres with necks along the GammaN and GammaL directions, respectively. The nonlinear increase of T-c(P) is connected with the non-linear variation of the radius [k(F)(P)] of the Fermi surface neck at high pressure. Our results indicate that, Li is a one-band rather than a one-electron metal. The electron-phonon interaction parameter (lambda) and its variation under pressure are structure independent in lithium, and Li is an electron-phonon mediated superconductor.