Pseudopotential plane-wave calculations were used to study the B interstitial in various ionic configurations and charge states. For all charge states, the ground state was a B-Si pair in which the B atom was close to a substitutional site and the Si atom was in a nearby tetrahedral position. The defect had the negative-U property and exhibited a symmetry-lowering distortion. Several metastable configurations were close with regard to their formation energy.

Theoretical Studies of Interstitial Boron Defects in Silicon M.Hakala, M.J.Puska, R.M.Nieminen: Physica B, 1999, 273-274, 268-70