Quantifying Dynamic Tilting in Halide Perovskites: Chemical Trends and Local Correlations

Halide perovskiteshave emerged as one of the most interestingmaterials for optoelectronic applications due to their favorable properties,such as defect tolerance and long charge carrier lifetimes, whichare attributed to their dynamic softness. However, this softness hasled to apparent disagreements between the local instantaneous andglobal average structures of these materials. In this study, we rationalizethis situation through an assessment of the local tilt angles of octahedrain the perovskite structure using large-scale molecular dynamics simulationsbased on machine-learned potentials trained using density functionaltheory calculations. We compare structural properties given by differentdensity functionals [local density approximation, PBE, PBE + D3, PBEsol,strongly constrained and appropriately normed (SCAN), SCAN + rVV10,and van der Waals density functional with consistent exchange] andestablish trends across a family of CsMX3 perovskites withM = Sn or Pb and X = Cl, Br or I. Notably, we demonstrate strong short-rangeordering in the cubic phase of halide perovskites. This ordering isreminiscent of the tetragonal phase and provides the bridge betweenthe disordered local structure and the global cubic arrangement. Ourresults provide a deeper understanding of the structural propertiesof halide perovskites and their local distortions, which is crucialfor further understanding their optoelectronic properties.