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

We theoretically studied the phase transition between the cubic-diamond and β-Sn structures for the Si0.5Ge0.5 alloy. We performed first principles calculations based on the density-functional theory, using the local-density approximation, and the variable cell shape molecular dynamics approach. The alloy was modeled using an ordered zincblende type lattice, and we obtained a transition pressure of 8.35 GPa. We also calculated the enthalpy curves at zero as well as at the transition pressure. At zero pressure, the enthalpy 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 enthalpy barrier is still 0.018 Ry/atom, a sign of the strong first order character of this phase transformation.