Local-density-functional pseudopotential theory was used to investigate native defects in diamond, their structure, electronic, vibrational, and diffusive properties. It was found that the only truly stable structure for an interstitial atom to be the 100 split interstitial defect. This conclusion holds in the neutral, -1, +1 and +2 charge states. The multiplet structure of this defect was analyzed, showing 1B1 to be the lowest in energy. However, a Jahn-Teller distortion was also possible in all but the +2 charge state, giving 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. An upper bound for the energy barrier to the motion of the 100 split interstitial was found to be 1.7eV. This was lower than that of vacancy diffusion although movement of interstitial atoms was usually ignored in considering self-diffusion. For the vacancy in diamond, it was found that the surrounding four atoms relax outwards by 0.2 in both the neutral and negative charge states. The neutral vacancy undergoes a Jahn-Teller distortion with an energy gain of 0.36eV. This effect was known to be dynamic at room temperature. For the negative vacancy, 4A2 was deduced to be the ground state and the transition energy to 4T1 was shown to be 3.3eV; in good agreement with the observed ND1 band at 3.149eV. Energies of other multiplets were estimated. The migration energies of the neutral and negative vacancies were found to be 2.8 and 3.4eV, respectively. The formation energy for a vacancy-100 split interstitial pair was calculated to be 20eV.

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