Ab initio calculation of high pressure phases and electronic properties of CuInSe2

We used an ab initio method to calculate the high pressure phases of CuInSe2. By using the experimentally suggested phases, the enthalpy difference showed that the I 4 ̄ 2 d structure transforms into F m 3 ̄ m at 12 GPa and then into Cmcm at 42 GPa. The volume reductions at each phase transition are 13.9% and 1.9% respectively, compared with 11% and 1% from experiments. By using the sX-LDA functional, we found that the bandgap in the I 4 ̄ 2 d structure increases at the rate of 39.6 meV/GPa, in fair agreement with photoabsorption experiments. The band gap is closed in the F m 3 ̄ m and Cmcm structures. The bond lengths between Cu–Se and In–Se were investigated. We found that the bond lengths can be related to the behavior of the energy gap under high pressure. The path of transformation from F m 3 ̄ m to Cmcm was proposed. The energy barrier between the two phases was estimated. The upper bound of the energy barrier is 17 meV which is equivalent to 198 K. This finding can explain the existence of two phases at room temperature reported by experimental study.