Ab initio study of vacancies in cubic BN under pressure

We investigate, through first-principles calculations, the pressure dependence of formation volumes and formation enthalpies of boron and nitrogen vacancies ( V B , V N ) in cubic boron nitride ( c -BN) using a supercell approach. We find that V B 3 − and V N 3 + have the lowest formation enthalpy and −3 and +3 can be considered as the dominant charges occurring in V B and V N at ambient pressure, respectively. And the charge states which have the lowest formation enthalpies do not change with pressure in the pressure range from 0 to 20 GPa. The formation enthalpy decreases with pressure for V B , while for V N it exhibits positive dependence of the formation enthalpy on pressure. Energy levels of defects under different pressures are also discussed. Our results suggest that for V N , pressure can strengthen its conductivity, while for V B , pressure effect is not obvious in our investigated pressure range.