Theoretical investigation of the pressure induced cubic-diamond-beta-tin phase transition in the Si0.5Ge0.5

We theoretically studied the phase transition between the cubic-diamond and beta -Sn structures for the Si0.5Ge0.5 alloy. We performed first principle s calculations based on the density,functional theory, using the local-dens ity approximation, and the variable cell shape molecular dynamics approach. The alloy was modeled using an ordered zincblende type lattice, and we obt ained a transition pressure of 8.35 GPa. We also calculated the enthalpy cu rves at zero as well as at the transition pressure. At zero pressure, the e nthalpy difference between the two phases is 0.016 Ry/atom, and there is a barrier of approximately 0.026 Ry/atom. At the transition pressure, the ent halpy barrier is still 0.018 Ry/atom, a sign of the strong first order char acter of this phase transformation. (C) 2001 Published by Elsevier Science Ltd.