A density functional theory study of models for the N3 and OK1 EPR centres in diamond

The defects observed in natural and synthetic diamonds provide a fingerprint of their differing growth conditions, as well as the thermal and mechanical processes they have experienced. Of the first row elements it is perhaps surprising that little evidence exists for oxygen in the form of distributed point-defects. Paramagnetic centres labelled N3 and OK1 have been assigned to two structural arrangements of pairs of substitutional nitrogen and oxygen, but there is no direct evidence for the involvement of the oxygen. In this paper we present the results of density functional simulations of N-O pairs in diamond, and review them in light of the experimental evidence. We also present analysis for other structures proposed in the literature (Ti-N, Ti-V-N, NV2 and NVO), and show that none are particularly plausible.