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Zero-temperature generalized phase diagram of the 4d transition metals under pressure C. Cazorla,1,2,3 D. Alf,1,2,3,4 and M. J. Gillan1,2,3

Summary: Zero-temperature generalized phase diagram of the 4d transition metals under pressure
C. Cazorla,1,2,3 D. Alfè,1,2,3,4 and M. J. Gillan1,2,3
1London Centre for Nanotechnology, UCL, London WC1H OAH, United Kingdom
2Department of Physics and Astronomy, UCL, London WC1E 6BT, United Kingdom
3Materials Simulation Laboratory, London WC1E 6BT, United Kingdom
4Department of Earth Sciences, UCL, London, WC1E 6BT, United Kingdom
Received 13 March 2008; published 4 June 2008
We use an accurate implementation of density-functional theory to calculate the zero-temperature general-
ized 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 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.


Source: Alfè, Dario - Departments of Earth Sciences & Physics and Astronomy, University College London


Collections: Physics; Geosciences