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 (243 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 α2F  . Although the initial pressure-induced transverse T1T1 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 (1 0 0).