Electronic, vibrational, and superconducting properties of CaBeSi: First-principles calculations

We report first-principles calculations on the normal and superconducting state of CaBexSi2-x (x=1), in the framework of density-functional theory for superconductors. CaBeSi is isostructural and isoelectronic to MgB2 and this makes possible a direct comparison of the electronic and vibrational properties and the electron-phonon interaction of the two materials. Despite many similarities with MgB2 (e.g., sigma and pi bands at the Fermi level and an even larger density of states), according to our calculations CaBeSi has a very low critical temperature T-c approximate to 0.4 K consistent with the experiment. CaBeSi exhibits a complex gap structure, with three gaps at the Fermi level: besides the sigma and pi gaps (present also in MgB2), the appearance of a third gap is related to the anisotropy of the Coulomb repulsion, acting in different ways on the bonding and antibonding electronic pi states.