A first-principles study of MgB2: the effect of pressure and substitution

We performed a first-principles calculation of the electronic band structure of MgB2, a superconductor discovered recently, by employing a full-potential linear muffin-tin orbital method. In advance, the influences of the lattice parameter on the electronic structure are investigated with different volumes and c/a ratios. The effects of substitution on the electronic structure are discussed in relation to the variation of the lattice parameters and electron filling which is investigated via a Mg pseudo-atom. The variations of the two-dimensional covalent σ-band and three-dimensional metal π-band are investigated in detail at several high-symmetry points of the Brillouin zone (BZ). These results show that the variations of the electronic structure of MgB2 are mainly determined by the effect of the c/a ratio. Considering the variation of the Fermi surface at the M and Γ points of the BZ, the corresponding electronic topological transition (ETT) induced by the lattice and doping are discussed. The ETT at the M point should be related to the structural phase transition in AlxMg1-xB. (author)