Motivated by this evidence for [F-O-O-F] anion ordering along ⟨100⟩ strings in ReO 3 -structured NbO 2 F [97], we next consider whether ReO 3 -type TiOF 2 is predicted to exhibit analogous [O-F-F-O] ordering. To explore this possibility, we performed two sets of calculations. First, we used our GA-structure-prediction scheme with our DFT-derived cluster-expansion model to generate a 6 × 6 × 6 supercell, with this supercell size chosen to accommodate anion orderings with a ×3 unit cell repeat distance. We then analysed the resulting structure to determine the relative prevalence of different ⟨100⟩ orderings. Second, we computed DFT geometry-optimised energies for three sets of TiOF 2 structures with different supercell sizes (2 × 2 × 2, 3 × 3 × 3, and 4 × 4 × 4) and different ⟨100⟩ anion orderings, to determine whether any of these ⟨100⟩ anion orderings is sufficiently energetically favoured to predict general anion ordering.