You convert the CIF into a POSCAR or .in file. The cubic cell allows for fast k-point sampling. However, note that DFT often requires relaxing the structure (especially the H atoms of FA, which are missing in basic CIFs).

A CIF file is the universal text-based standard established by the International Union of Crystallography (IUCr) for sharing structural data. For FAPbI3, the file bridges the gap between raw experimental X-ray diffraction (XRD) data and 3D atomic visualization software.

Using the CIF, software like VESTA or Mercury calculates the powder X-ray diffraction pattern. Key peaks for α-FAPbI₃:

Finding the right fapbi3 cif file is the first and critical step in accurately modeling this high-performance perovskite. Whether you choose a high-temperature experimental structure from the COD, an optimized DFT structure from a GitHub repository, or a commercial file from the ICSD, you must always verify the phase (α vs. δ) and the atomic occupancy to avoid serious errors.