By using a first-principles pseudopotential approach, it was shown that the lowest-energy configuration for a neutral Si interstitial was the (011) dumb-bell. Another local minimum-energy atomic configuration, with a very similar energy, was found. This had very low symmetry, and was therefore multiply degenerate. Other high-symmetry configurations were found to be mechanically unstable. Further molecular dynamics simulations were used to study self-interstitial migration. These revealed several possible mechanisms, and a tendency for an atom to become excited and execute several correlated jumps through the structure before being recaptured into the minimum energy state. Both the excitation and recapture processes appeared to be thermally activated, but the number of jumps was larger at low temperatures and the overall migration was athermal.

S.J.Clark, G.J.Ackland: Physical Review B, 1997, 56[1], 47-50