To further explore the nature of O/F disorder in ReO 3type TiOF 2 , we conducted a computational analysis of all possible 2 × 2 × 2 TiOF 2 supercells (Ti 8 O 8 F 16 ), consisting of 2664 distinct symmetry inequivalent O/F configurations. To efficiently compute the relative energies of all 2664 structures, we first performed DFT calculations on a subset of 65 structures and used these results to fit a cluster-expansion model, as described in the Methods section. This cluster-expansion model was then used to calculate the energies of all 2664 2 × 2 × 2 supercells. The resulting configurational density of states for all 2 × 2 × 2 TiOF 2 supercells (Fig. ) reveals an energy difference of 0.94 eV per formula unit between the configurations with the lowest and highest energies. This energy variation between different anion configurations indicates a strong energetic preference for certain short-range anion configurations over others, consistent with short-range ordering. This finding contradicts the previously proposed structural model that O and F positions in ReO 3 -type TiOF 2 are completely uncorrelated , which instead implies equal energies for all 2 × 2 × 2 TiOF 2 cells.