Transition pressures and enthalpy barriers for the cubic diamond->beta-tin transition in Si and Ge under non-hydrostatic conditions

We present an ab-initio study of the phase transition cubic diamond->beta-tin in Si and Ge under hydrostatic and non-hydrostatic pressure. For this purpose we have developed a new method to calculate the influence of non-hydrostatic pressure components not only on the transition pressure but also on the enthalpy barriers between the phases. The calculations were performed using the plane-wave pseudopotential approach to the density-functional theory within the local-density and the generalized-gradient approximation implemented in VASP. We find good agreement with available experimental and other theoretical data.