A novel model was proposed for a self-interstitial defect in crystalline Si. It involved four Si interstitials such that all of the Si atoms were 4-fold coordinated (in contrast to previously proposed models) and was characterized by the presence of 5-, 6-, and 7-membered atomic rings. The total energy, relaxed atomic configuration, and electronic structure of the defect were determined by using the transferable semi-empirical tight-binding method.

N.Arai, S.Takeda, M.Kohyama: Physical Review Letters, 1997, 78[22], 4265-8