The role of Coulomb interaction in the superconducting properties of CaC6 and H under pressure

Superconductivity in intercalated graphite CaC6 and H under extreme pressure is discussed in the framework of superconducting density functional theory. A detailed analysis of how the electron-phonon and electron-electron interactions combine together to determine the superconducting gap and critical temperature (Tc) of these systems is presented. In particular, we discuss the effect on the calculated Tc of the anisotropy of the electron-phonon interaction and of the different approximations for screening the Coulomb repulsion. These results contribute to the understanding of multigap and anisotropic superconductivity, which has received a lot of attention since the discovery of MgB2, and show how it is possible to describe the superconducting properties of real materials on a fully ab initio basis. © 2009 IOP Publishing Ltd.