On the Development of a Classical Interatomic Potential for MAPbBr3

We develop a classical interatomic potential for MAPBr. The model belongs to the class of MYP force-fields for hybrid perovskites based on two-body Buckhingam-Coulomb and dispersive terms to describe organic-inorganic interactions and already successfully applied to MAPI. The model calibration is based on a simplified procedure able to extend one existing parameterization to a different halide by suitable scaling of selected subgroups of parameters. The main static and dynamical properties of MAPBr are well reproduced by the developed model: the lattice constant, cohesive energy curve, bulk modulus, energy barriers for cation rotations (both static and dynamic), the phase transition temperatures and structural parameters evolution with temperature. The model also provides valid relationship between MAPBr and MAPI: MAPBr has shorter lattice constant, higher cohesive energy, lower phase transition temperatures, and lager anisotropy in orthorhombic phase. The good comparison extends also to the vibrational properties at finite temperatures that have been benchmarked on experimental and DFT results. The developed MAPBr model is further used to calculate the MA dynamics in MAPBr at room temperature finding a reorientation time of ~3ps in good agreement with experimental data. Present work represents an important step towards the large-scale atomistic modeling of MAPBr and the development of a general class of force fields for hybrid perovskites.