Origin of Strong Coupling in Lithium under Pressure

In an attempt to provide a clearer understanding of the impressive increase in Tc under pressure in elemental Li, linear response calculation of the phonon dispersion curves, electron-phonon matrix elements, phonon linewidths and mode λ’s have been carried out on a finer mesh (24 in the Brillouin zone) than done previously, for the volume corresponding to 20 GPa pressure. The result illustrates the great need for a fine mesh (even finer than this) for converged results of λ and the spectral function αF . Although the initial pressure-induced transverse T1 phonon instability (in harmonic approximation) near the symmetry point K has dominated attention, the current results show that the high value of Tc gets strong contributions from elsewhere in the zone, particularly from the longitudinal mode along (100).