Physical Review Letters
Linear combination of atomic orbital—molecular orbital cluster calculations using extended Hückel theory suggest that the interstitial carbon atom in diamond prefers an "interstitialcy" configuration. The predicted minimum-energy configuration changes with charge state, providing a possible example of the Bourgoin mechanism for "athermal" migration of the interstitial in the presence of ionizing radiation.
G.D. Watkins, R.P. Messmer, C. Weigel+, D. Peak, and J.W. Corbett "Properties of the Interstitial in the Diamond-Type Lattice," Physical Review Letters 27, 1573-1575 (1971).