It was noted that both C and Si interstitial atoms were mobile, and became trapped at other defects (thus altering their properties) or displaced impurity atoms into interstitial sites. An approximate molecular orbital procedure, which incorporated Car-Parrinello like dynamics, was used to model the structure of Si and C interstitials. By displacing them along their possible migration paths, and by allowing them to relax back into their stable sites, the details of low-energy migration routes were calculated. It was found that the neutrally charged Si interstitial occupied a (110) split site, but with the axis displaced (along the z-direction) away from the nearest pair of Si neighbors. Negative and singly positively charged interstitials occupied the same sites but, when doubly positively charged, the hexagonal sites were more stable. The migration path of the neutral Si interstitial involved a complex route, with an activation energy of 0.2eV.

A.Mainwood: Materials Science Forum, 1995, 196-201, 1589-94