In the absence of transition metals, it was assumed that the first stage of nitrogen aggregation, where close neighbour nitrogen pairs were formed, was mediated by NV defects. Density functional theory was used here to explore the barriers to NV diffusion. It was concluded that the barrier was about 5eV when there was a ready source of vacancies and that this barrier was weakly dependent upon pressure.

On the Diffusion of NV Defects in Diamond. Pinto, H., Jones, R., Palmer, D.W., Goss, J.P., Briddon, P.R., Öberg, S.: Physica Status Solidi A, 2012, 209[9], 1765-8