Electronic structural properties and superconductivity of diborides in the MgB2 structure

We calculate the critical temperature T-c of a wide range of diborides which have the same crystal structure as MgB2. Their electronic structure is also calculated in the framework of the local density approximation method of density functional theory by using the pseudopotential plane wave approach. The Hopfield factors eta of these materials are calculated by the frozen phonon method. Our results show that most of these diborides have low 77, and hence low or no T-c; this is consistent with experimental observations. The most important result of our calculation is that AgB2 and AuB2 have higher T-c than MgB2. The high T-c of these two materials comes from the combination of the high density of states and high deformation potential of the sigma bands.