Anisotropic gap of superconducting CaC6: A first-principles density functional calculation

We report first-principles calculations of the superconducting properties of CaC6, obtained within the density functional theory of superconductivity. We find a moderately anisotropic gap which is larger on the Fermi surface sheet with interlayer and Ca character compared with isotropic calculations. Our calculated anisotropy improves the agreement with specific heat experiments and is consistent with recent tunneling experiments. In contrast to MgB2, we do not find multigap superconductivity but, instead, a continuous spread of gap values.