Several metastable structures with energy less than 1 meV difference from the structure used to plot the transition level diagrams were identified using the ShakeNBreak method. Their relative energies are shown in Figure . The charge localisation is different between the structures, with Figure showing the difference between the 'unperturbed" (no distortions) and lowest energy (-50% bond distortion) structures. The energy difference is so small that at finite temperature, it is likely that the real charge density is some combination of the two, indicating a reasonably delocalised charge density (as stated in the main text).