Local density functional pseudopotential theory was used to investigate the structural, electronic, vibrational, and diffusive properties of native defects. It was found that the only truly stable structure for an interstitial atom was the <100> split interstitial defect. This conclusion held for the neutral, -1, +1, and +2 charge states. The multiplet structure of this defect was analyzed, and it was found that 1B1 was the lowest in energy. However, a Jahn-Teller distortion was also possible in all but the +2 charge state, and this led to considerable reductions in energy (0.6eV for the neutral case). The tetrahedral, hexagonal, bond-centered, and <110> split interstitial structures were shown to be unstable. The upper bound on the energy barrier to motion of the <100> split interstitial was found to be 1.7eV. This value was lower than that for vacancy diffusion, although the movement of interstitial atoms was usually ignored when considering self-diffusion. In the case of the vacancy in diamond, it was found that the surrounding 4 atoms relaxed outwards by 0.02nm in both the neutral and negative charge states. The neutral vacancy underwent a Jahn-Teller distortion with an energy gain of 0.36eV. This effect was known to be dynamic at room temperature. In the case of the negative vacancy, 4A2 was the ground state and the transition energy to 4T1 was 3.3eV; in good agreement with an observed ND1 band at 3.149eV. It was found that the migration energies of the neutral and negative vacancies were 2.8 and 3.4eV, respectively. Finally, the formation energy of a vacancy-<100> split interstitial pair was calculated to be 20eV.

Ab initio Investigation of the Native Defects in Diamond and Self-Diffusion. S.J.Breuer, P.R.Briddon: Physical Review B, 1995, 51[11], 6984-94