A Reasonable DFT Calculation Method for Hybrid Organic-Inorganic Halide Perovskites

Hybrid Organic-Inorganic Perovskites (HOIP) have received a great deal of attention as a key material for applications like solar cells and light emitting devices because of their many advantages, in spite of their stability and toxicity issues. Attempting to discover and characterize novel HOIPs using just an experimental approach would be prohibitively time-and-cost-consuming. Using theoretical or empirical calculations would greatly help. For these reasons, HOIP has been actively investigated using DFT (Density Functional Theory) calculations, which have significantly reduced research time and cost. However, the input model structure treatment needs to be standardized to avoid unnecessary complications. For this purpose, a sort of optimization of DFT calculation protocols for HOIPs is essential, because DFT calculation results are greatly affected by the input model structure arrangements and exchange-correlation functionals. In this paper, we used DFT to calculate the band gap, formation energy, and effective mass of the well-known cubic perovskite structure, methylammonium lead iodide (CH3NH3PbI3: MAPbI3) with and without the van der Waals function and SOC (Spin Orbit Coupling) and various geometrical molecule arrangements in the structure. In particular, the initial orientation of the ‘A’ site molecule in the input model structure was intensively investigated in terms of band gap, formation energy and effective mass. It was found that the relaxation-induced final structure was greatly influenced by the initial orientation of the molecule and thereby significantly affected the DFT-calculated result.