Stability of Diamond at Megabar Pressures

Abstract

AbstractThe stability of diamond at megabar pressures (1 Mbar = 100 GPa) is studied by means of ab‐initio simulations. Under hydrostatical pressure, diamond is found to be locally stable (i.e. a local enthalpy minimum) up to a pressure as high as 3000 GPa, where it is predicted to collapse into a sixfold coordinated metallic phase never considered so far. On the other hand, if a considerable uniaxial component is added to the stress tensor, as in diamond‐anvil‐cell experiments, a completely different scenario applies whereby much lower pressures are required to bring diamond to mechanical instability. Qualitative considerations on the maximum pressure achievable in diamond anvil cells are presented.