I am a research student in the perovskite solar cell research field and I want to use VASP software for the simulation.I am a very beginner at it. Currently I am doing band structure calculation and Ferroelectric and dielectric behavior of CH3NH3)3Bi2I9, Cs3Bi2I9 for suitability of solar cells using Vasp software. Some difficulties are facing me. could you please give some instructions and guidance regarding that analysis.