d of all sites and computing the fraction above the minimum threshold of 2.3 eV, denoted x min , and the fraction of defects in the optimal range of [2.3, 4.0] eV, denoted x rng . If the material contains any defects below the target range, the reduced metal oxide cannot readily be regenerated at the oxidation conditions relevant for STCH, and thus we require x min = 1. It may be ideal for all defects to fall within in the target range (x rng = 1) to increase capacity and defect mobility, but these considerations are beyond the scope of this study. In practice, only one defect needs to fall within the targeted range to be considered a promising STCH material (x rng > 0).