Experimental (Exp; 300K) and simulated (Sim) X-ray scattering function S(q) at the (H, K, L=1.5) reciprocal space plane in the average cubic Pm3m phase of FAPbBr3. The figures are divided into four quadrants: top left, total experimental S(q); top right, experimentally derived QEDS; bottom left, simulated QEDS obtained by fitting the experimentally derived QEDS data to a phenomenological model; bottom right, MD-simulated S(q, E) integrated over the QEDS energy window, that is, 1meV < E < 1meV. S(q) intensities in each quadrant are normalized to 1, with the two-dimensional images coloured via bilinear interpolation. MD trajectories simulated at 340K for MAPbBr3 and 250K for FAPbBr3 were chosen as they best match the experimental 300K data due to an offset between the experimentally and MD-simulated phase transition temperatures (Supplementary Note 8).
