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 (T-c) of these systems is presented. In particular, we discuss the effect on the calculated T-c 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.