Electronic structure of (organic)-inorganic metal halide perovskites: the dilemma of choosing the right functional*

Organic-inorganic metal halide perovskites are materials widely studied for their light-harvesting properties. Owing to the interplay between strong electron-electron interaction and spin-orbit coupling (SOC), their theoretical investigation is still a challenge. Here, we evaluate methodologies to compute the electronic structure of APbI₃, where A can be organic like MA or FA, or inorganic like Cs, and their precursor PbI₂. To this extent, we investigate several approaches within density functional theory (DFT) and many-body perturbation theory (MBPT), taking into account SOC effects. Hybrid functionals, such as PBE0 and HSE, are at the center of the investigation, since they can provide results as accurate as MBPT at a lower computational cost. Hence, we explore several nonempirical methods to tune their parameters. Additionally, at the MBPT level, we investigate the dependence of the calculations from the DFT starting point. All the calculations are performed with the full-potential all-electron computer package exciting. We observe that properly tuned hybrid functionals are the most suitable functionals to compute the electronic structure of APbI₃ and PbI₂.