Calculated superconductive properties of Li and Na under pressure

Using ab initio calculations of electronic structures and electron-phonon coupling in each phonon state we examine the superconductive properties of Li and Na under pressure. From the Eliashberg equations it is found that a Coulomb pseudopotential parameter (mu(*)) of "usual" magnitude (0.13) yields T-c values for fcc-Li close to experiments, and they also agree well with recent similar calculations by Tse [J. Phys.: Condens. Matter 17, S911 (2005)], Maheswari [J. Phys. Soc. Jpn. 74, 3227 (2005)], and Kasinathan [Phys. Rev. Lett. 96, 047004 (2006)]. Consequently, the T-c values for fcc-Li predicted earlier by us [Phys. Rev. Lett. 86, 1816 (2001)] are clearly too high, and reasons for this are discussed. The calculations for sodium suggest that superconductivity should not be observed in the fcc phase, except, maybe very close to the fcc-cI16 transition, but then with T-c at most similar to 1 K. Both fcc-Li and fcc-Na become dynamically unstable (soft modes) as the pressure exceeds similar to 40 and similar to 90 GPa, respectively.