Electronic, dynamical and superconducting properties of MgB2: doping, surface and pressure effects

We report a detailed first-principles local-density-functional investigation of the structural, electronic, dynamical and superconducting properties of MgB2 focusing on different aspects related to this material. In particular, we examine Al doping, as well as reduced dimensionality and pressure effects on the electronic and superconducting properties of this compound. Our ab initio calculations for the case of 50% Al doping are able to correctly reproduce the measured frequencies of the E-2g phonon and explain the disappearance of superconductivity in terms of filling effects on both carrier concentration and electron-phonon coupling. The surface study shows that an enhanced density of states at the Fermi level is found in the B-terminated case. However, we find the Mg-terminated surface to be the most stable structure in the whole range admitted by the chemical potentials, in agreement with very recent experimental results. Finally, the study of the E-2g phonon frequency under pressure is able to explain the critical temperature lowering under applied pressure.