Comparative Study of the Electronic Structure of Alkaline-earth Borides   (MeB2; Me=Mg, Al, Zr, Nb, and Ta) and their Normal-State Conductivity
  By means of density functional theory the electronic structure of the MgB2 superconductor was characterised and compared with that of the related iso-structural systems: AlB2, ZrB2, NbB2, and TaB2. Using the full-potential linearized augmented plane waves (FP-LAPW) method and the generalised gradient approximation, the electronic density distribution, density of states, and band structures were obtained for these compounds. The electrical conductivity, which cannot be easily measured in the c-direction, was calculated, in the relaxation time approximation using band structure results. It was found that the two-dimensional (2D) crystal structure character of these metallic diborides is also reflected in the electronic charge distribution. This 2D pattern is not completely seen in the electrical conductivity as it is, for instance, in the superconductor high Tc cuprates. Indeed, it was found that, by the electrical conductivity calculations, all these compounds have a bulk, yet anisotropic, conductivity. 
Pablo de la Mora, Miguel Castro and Gustavo Tavizon