A. B. Belonoshko, L. Burakovsky, S. P. Chen, B. Johansson, A. S. Mikhaylushkin, D. L. Preston, S. I. Simak, and D. C. Swift,
Phys. Rev. Lett. 100, 135701 (2008).
The Gibbs free energies of
bcc and
fcc Mo are calculated from first principles in the quasiharmonic approximation in the pressure range from 350 to 850 GPa at room temperatures up to 7500 K. It is found that Mo, stable in the
bcc phase at low temperatures, has lower free energy in the fcc structure than in the
bcc phase at elevated temperatures. Our density-functional-theory-based molecular dynamics simulations demonstrate that
fcc melts at higher than
bcc temperatures above 1.5 Mbar. Our calculated melting temperatures and
bcc-fcc boundary are consistent with the Mo Hugoniot sound speed measurements. We find that melting occurs at temperatures significantly above the
bcc-fcc boundary. This suggests an explanation of the recent diamond anvil cell experiments, which find a phase boundary in the vicinity of our extrapolated
bcc-fcc boundary.