12 Possible Orientations of organic Formamidinium cation and its structural analysis by First Principles calculations using Van der Waals-Density functional Theory

Formamidinium lead iodide (FAPbI3) is a promising and low-cost alternative absorber material in the organic-inorganic perovskites solar cells area. Recently, the theoretical study has been widely used to understand the mechanism behind the structural and phase change in the perovskite crystal structure. In this work, we systematically performed the first principle density functional theory calculations (DFT) using van der Waals (vdW) interaction (Tkatchenko–Scheffler scheme, TS) for 12 possible orientations of organic Formamidinium (FA) cation use as basis of xy, yz, xz plane (each plane has 4 possible orientation) in the cubic cage in order to investigate the structural behavior of FAPbI3 perovskites. Here, the theoretically obtained calculation result shows a similar trend in the lattice parameters, distribution of the electron density difference (EDD), total energy, unit cell volume and the displacement of iodide atoms for all possible 12 orientations of FA cation.