First-principles local-density functional theory was used to investigate the properties of di-interstitial, tri-interstitial and tetra-interstitial structures. It was shown that a tri-interstitial defect could account for many of the fundamental properties of the I1/W optical centre in irradiated and annealed samples.

Interstitial Aggregates and a New Model for the I1/W Optical Centre in Silicon B.J.Coomer, J.P.Goss, R.Jones, S.Oberg, P.R.Briddon: Physica B, 1999, 273-274, 505-8