To explain this latter observation, we take the lowestenergy structure which contains an oxygen dimer, and rerelax it after forcing the oxygen ions back to their initial FIG. . The histograms show site-projected magnetic moments in a dimer-free structure with a migrated Ni-ion for both oxygen ions (left) and nickel ions (right). The structural schematic beneath highlights the structural changes and energy change when the O -ions are brought together to form a dimer. positions, i.e. removing the dimer. The site-projected magnetic moments for this structure are shown in fig. . Two oxygen atoms carry site-projected magnetic moments commensurate with the unpaired spin expected from an oxidized oxide ion (two holes localized on two oxide ions), and the migrated nickel ion now appears in the 2+ oxidation state. Formulated as a defect reaction relative to the layered structure, this can be described as