Electronic Structure Theory Research Of Cuprous Oxide Under Hydrostatic Pressure

In order to understand the phase transition and driving mechanism of cubic cuprous oxide under hydrostatic pressure. We have systematically investigated the phase transition, elastic stability and phonon spectrum of cuprous oxide under hydrostatic pressure using first-principles calculation method. The main conclusions are summarized as follows:(1) The phase transition from cubic structure to hexagonal structure is observed in curprite under hydrostatic pressure. The volume of curprite changed discontinuously during the phase transition region which indicates that the phase transition is a first-order phase transition.(2) From the perspective of elastic, elastic constants C44 and C11- C12 of cubic curprite decrease continuously with the pressure, and became negative in the end, which means elastic instability before the phase transition. Therefore, the phase transition from cubic structure to hexagonal structure is caused by elastic instability.(3) From the perspective of dynamic, phonon spectrum of cubic curprite appeared "empty frequency" when the pressure reaches 18 GPa, which means dynamic stability in the cubic curprite. Therefore, dynamic stability near phase transition leads to the phase transition from cubic structure to hexagonal structure.(4) The bottom of the conduction band and the top of the valence band of cubic curprite are at Γ point. With the pressure increase, the band gap increase and the degeneracy of bottom of conduction band changed from 2 to 3. Hexagonal structure is a semi-metalic phase with the conduction band and valence band overlap together.(5) The ground state binding energy(eV) of copper atomic d orbitals, the corresponding band gap, the relationship between the state density and energy were obtained by GGA, GGA+U and HSE(GGA+U) methods, which illustrated the fact that the bigger the binding energy of d orbitals, the more accurate the band gap.