Pressure-Induced Cubic-to-Hexagonal Phase Transition in Cu₂O

Phase transition and band structure of Cu₂O are systematically investigated by using the HSE06 range-separated hybrid functional. Cubic Cu₂O under pressure transforms to the metastable hexagonal phase. Our further investigations reveal that the first-order phase transition is driven by the elastic and dynamical instabilities. Furthermore, the stable band gap of cubic phase is always direct and greatly enhanced by pressure, whereas the hexagonal phase shows the semi-metallic band structure.