  Halide perovskites have emerged as one of the most interesting materials for
optoelectronic applications due to their favorable properties, such as
defect-tolerance and long charge carrier lifetimes, which are attributed to
their dynamic softness. However, this softness has led to apparent
disagreements between the local instantaneous and global average structures of
these materials. In this work, we assess the local tilt angles of octahedra in
the perovskite structure through large-scale molecular dynamics simulations
using machine learned potentials based on density functional theory. We compare
structural properties given by different density functionals, namely PBE,
PBEsol, SCAN, and vdW-DF-cx, and establish trends across a family of CsMX3 with
M=Sn or Pb and X=Cl, Br or I perovskites. Notably, we demonstrate a strong
short-range ordering that persists even in the cubic phase of halide
perovskites. This ordering is reminiscent of the tetragonal phase and bridges
the disordered local structure and the global cubic arrangement. Our results
provide a deeper understanding of the structural properties of halide
perovskites and their local distortions, which is crucial for further
understanding their optoelectronic properties.
