Electronic structure and electric field gradient in MgB2 under pressure: an ab initio study

Abstract

We report here ab initio density functional theory studyof the electronic band structure and electric field gradient(EFG) in MgB2 under pressure. The band structurecalculations are in agreement with other recent calculations. The superconductivity in MgB2 is related to and dominatedby the existence of boron σ px,y-band holes at theΓ point, with negligible contribution from the Mgions. The character of the σ band is unchanged evenafter application of pressure, although there is a shift ofposition and an increase of dispersion. The calculated densityof states decreases with pressure which, in conjunction withthe Bardeen-Cooper-Schrieffer theory, agrees with thetrend of the experimental Tc versus pressure data. Thebroad bump in Tc(P) data observed by Tissen et al near9 GPa is not indicated in the present band structure study. TheEFG at the B site is nearly constant as a function of pressureand that of Mg changes by ~34% over the pressurerange considered. The present result indicates that the Belectronic system does not change much under pressure up to~38 GPa, which confirms one reported study but disagreeswith the other.