Zero-temperature generalized phase diagram of the 4d transition metals under pressure

We use an accurate implementation of density-functional theory to calculate the zero-temperature generalized phase diagram of the 4d series of transition metals from Y to Pd as a function of pressure P and atomic number Z. The implementation used is full-potential linearized augmented plane waves, and we employ the exchange-correlation functional recently developed by Wu and Cohen. For each element, we obtain the ground-state energy for several crystal structures over a range of volumes, the energy being converged with respect to all technical parameters to within similar to 1 meV/atom. The calculated transition pressures for all the elements and all transitions we have found are compared with experiment wherever possible, and we discuss the origin of the significant discrepancies. Agreement with experiment for the zero-temperature equation of state is generally excellent. The generalized phase diagram of the 4d series shows that the major boundaries slope toward lower Z with increasing P for the early elements, as expected from the pressure induced transfer of electrons from sp states to d states, but are almost independent of P for the later elements. Our results for Mo indicate a transition from body-centered cubic to face-centered cubic, rather than the bcc-hcp transition expected from sp-d transfer.