Given the relatively low-pressure transition to a rhombohedral structure for NbO2F, DFT+U calculations were also performed at elevated external pressures using a rhombohedral unit cell (Fig. ) in order to allow additional degrees of freedom for octahedral tilting and distortion during the geometry optimisations. The quality of the rhombohedral geometry optimisations was evaluated by comparison with experimental results for NbO2F (Fig. ). For the cubic structure at ambient pressure there is good agreement between the experimental and computational results. However, at elevated pressure, the lattice parameter is slightly underestimated, and the cell angle overestimated on the order of 2 o .