Non-Perturbative Finite Temperature Electronic Structure of Methyl-Ammonium Lead Iodide (MAPbI3) through a Physical Atomic Orbital Tight Binding Model

Halide perovskites show promising photovoltaic and optoelectronic properties, despite large, nonlinear lattice fluctuations at room temperature. Theoretical calculation of thermally disordered electronic structure requires accurate prediction of local electronic interactions in terms of atomic structure, but the length scales of such disorder are too large for plane wave DFT calculations. We present an atomic orbital tight binding model of MAPbI3 capable of extending the accuracy of ab initio calculations to the length and time scales of thermal disorder. Our model predicts the atomic orbital Hamiltonian from atomic structures using either physical fits or machine learning, including the fluctuations in orbital energy, bond geometry, and spin orbit coupling. Benchmarking against DFT shows quantitative accuracy of both individual matrix elements and overall band structure across a range of temperatures and phases. We present applications to temperature dependence of carrier mass and bandgap, as well as differentiating the relative effects of increased bond lengths and disorder on these quantities. Finally this model suggests methods for treating dynamical spin splitting, polaron formation, surfaces, defects, nanocrystals, and other materials.