Electronic structure, equation of state, and lattice dynamics of low-pressure Ge polymorphs

With the interest of obtaining more information on the low-energy phase diagram of germanium and its degree of similarity with silicon, we have performed first-principles calculations of the electronic structure and lattice dynamics of the R8, BC8, ST12, and hexagonal diamond structures of Ge. To aid future experimental investigation, we include predictions of the Raman-active frequencies of these phases as well as present the full phonon dispersion throughout the zone. Calculated equation of states within the local density approximation reveal a small pressure region where the R8 phase is energetically favored over the other metastable BC8 and ST12 structures, although the energy differences involved are relatively small and affected by the approximations used in the choice of pseudopotential.