FAPbI3_tetragonal&cubic

Initial structure of FAPbI3 of cubic phase was obtained through CIF file reported in previous report. While for tetragonal phase, no such CIF file could be found. Thus, we directly substitute Cs+ for FA+ in tetragonal phase CsPbI3, and then the resulting structure was relaxed through DFT calculation for the most stable structure. According to the usually inaccurate position of light element, we only apply structure relaxation calculation on FA+ while the Pb2+ and I- remain still.Structure relaxation and band-structure calculations are performed with plane-wave pseudopotential approach implemented in DS-PAW package. The exchange-correlation effects are concerned by PBE functional. The plane-wave cutoff energy was set to be 300.0 eV. The k-point number we set to be 5 × 5 × 5 for cubic phase and 4 × 4 × 5 for tetragonal phase respectively. Due to the heavy atom contained in perovskite materials, spin orbit coupling is included in DFT calculation for describing the real physical scenario.