Method

  All the defects considered here have been symmetry constrained - C_1h for N_iO_i, N_2iO, C_2v for N_i, etc. unless stated otherwise. However we also breached the symmetry of the defects and allowed them to relax; in every case they returned to the constrained symmetry structure. A variety of different cluster sizes have been used. Initial results were obtained using 113 atom clusters, and the final results shown here come from 134 atom clusters for the NNO work, and 148-152 atom clusters for the rest. The results are qualitatively identical, showing them to be independent of cluster size.