Full-potential study of structural and electronic properties of MB2-type metal diborides (M = Be, Mg and Ca)

Structural, electronic and bonding properties of BeB2 and CaB2 were studied using the full-potential linearized augmented plane-wave (FP-LAPW) method, based on the density functional theory implemented in the WIEN2k code and are compared with those of the isostructural superconductor MgB2. The exchange and correlation potential energies are treated using the local density approximation (LDA), The results are compared with available theoretical and experimental data. In particular, Our result of density of states at the Fermi level N(EF) for CaB2 equal to 0.993 states/(eV-f.u.) are found more close to recent pseudopotential result of Choi et al., which give 0.960 states/(eV-f.u.) and is different from 0.796 states/(eV-f.u.) as previously published result by Ravidran et al. We also evaluate the electronic structure of BeB2 in order to obtain further insight into its surprising difference from the superconducting MgB2 and therefore attempt to predict the nature of CaB2, one of the interesting candidates for the higher Tc.

Research highlights
► We give a detailed presentation of BeB2, MgB2 and CaB2 using the FP-LAPW method.
► The higher Tc is due to the raising of the value of the density at the EF level.
► The band structure of the superconducting MgB2 are due to the Boron 2p-states.
► CaB2 may be a superconducting compound due to his value of the density at EF.