First-order pressure-induced polyamorphism in germanium

We report on the pressure-induced phase transition in amorphous Germanium (a-Ge) using an ab initio constant pressure-relaxation simulation. a-Ge exhibits a first-order polyamorphic phase transition at 12.75 GPa with a discontinuous volume change of similar to19%. The transition pressure is also calculated from the Gibbs free-energy curves, and it is found that the transition occurs at 5.2 GPa in agreement, with the experimental result of 6 GPa. The pressure-induced delocalization of electronic and vibrational states is obtained.