Orthorhombic Structuresas Inorganic Halide PerovskiteModels for High-Throughput DFT Investigations

Although high-symmetry <i>Pm-3m</i> space group cubic models are computationally efficient for high-throughput density functional theory (DFT) calculations of inorganic ternary (ABX₃) halide perovskites (HPs), they frequently predict band gaps (<i>E</i>_g) that disagree with experiment. Conversely, while low-symmetry cubic polymorphous networks (PN) comprised of 160 to 320 atoms incur <i>significantly</i> greater computational cost, they predict <i>E</i>_g’s that are more closely aligned with experiment. In this study, we compare the DFT total energies and <i>E</i>_g’s predicted by four high-symmetry structure models (<i>Pnma</i> orthorhombic, <i>R3m</i> trigonal, <i>P4/mbm</i> tetragonal, and <i>Pm-3m</i> cubic) to cubic PNs for 5 experimentally characterized ternary HPs and find that the orthorhombic model computes <i>E</i>_g’s with the smallest MAD of 0.23 eV relative to the PNs. Pair distribution functions and DFT-computed total energies show that octahedral tilting, which is present in the 20-atom orthorhombic and 160-atom cubic PN models but not in the 5-atom cubic models, stabilizes all 5 compositions in our benchmarking set. We also find that imposing PN constraints when generating and optimizing these orthorhombic structures by fixing the unit cell lattice vectors and displacing the atoms prior to ionic relaxation with DFT, which we call the orthorhombic surrogate model (OSM), lowers the MAD of <i>E</i>_g predictions to 0.09 eV. Our OSM predicts the PN band gaps of an additional 95 theoretical inorganic ternary HPs with MAD of 0.08 eV, supporting its usage in high-throughput DFT investigations to closely estimate PN band gaps with much less computational expense.