BAND-GAPS OF DIAMOND UNDER ANISOTROPIC STRESS

Quasiparticle excitation energies are calculated using the GW method for diamond under hydrostatic pressures up to 500 GPa and for one tetragonal configuration under an assumed additional stress in the [001] direction. The self-energy operator is approximated with a model for the static screened Coulomb interaction and a plasmon pole approximation for the dynamically screened interaction. The band gaps increase with hydrostatic pressure. In contrast, the minimum gap decreases upon the application of additional [001] stress, with an extrapolated ultimate metallization pressure of 400 GPa, whereas current experimental extrapolations are for a transition at 700-900 GPa. The lower theoretical value is likely due to excessive anisotropy in the model for the applied stress.