Octahedral Dynamics and Local Symmetry in Hybrid Perovskite FAPbI ₃ under Thermal Excitation

High Resolution Image Download MS PowerPoint Slide Density functional theory (DFT) and ab initio molecular dynamics (AIMD) simulations have been employed to investigate the evolution of local motifs within the tetragonal phase of FAPbI 3 under thermal excitation. Our results reveal a distinct broadening in the distribution of PbI 6 octahedral volumes with increasing temperature, indicating a gradual breakdown of symmetry and emergence of diverse local environments. These octahedral volume distortions are primarily driven by the dynamic behavior of the FA cation, leading to softening of PbI 6 octahedra, evident from the calculated mean octahedral volume and Pb–I–Pb bond angles. The examination of the electronic structure confirmed that this dynamic structural phenomenon is directly responsible for the change in fundamental band gap value, highlighting the role of PbI 6 octahedra in modifying and modulating the electronic properties in FAPbI 3 . The results demonstrate the microscopic origin of thermally induced dynamical behavior to the macroscopic electronic properties and underscore the pivotal role of local motifs in hybrid perovskites.