A first-principles pseudopotential study of neutral self-interstitial defects was carried out, combined with calculations which were based upon Pandey's concerted exchange mechanism for self-diffusion. The energies and structures of the fully relaxed hexagonal, tetrahedral, split-(110), caged, split-(100) and bond-centred interstitials were calculated by using super-cells with up to 129 atoms. Results were obtained by using the local density approximation and the PW91 generalized gradient approximation for the exchange-correlation energy. Both the local density approximation and generalized gradient approximation functionals indicated that the hexagonal and split-(110) defects were the lowest-energy self-interstitials. The latter 2 defects were essentially degenerate in energy, with formation energies of about 3.3eV (local density approximation) and 3.80eV (generalized gradient approximation). The energy barriers were studied by calculating saddle-point structures, using a simple 'ridge-walking' method. The energy barrier to diffusive jumps between the hexagonal and split-(110) interstitial sites was calculated to be 0.15eV (local density approximation) or 0.20eV (generalized gradient approximation). The barrier between neighbouring hexagonal sites was 0.03eV (local density approximation) or 0.18eV (generalized gradient approximation). No low-energy path between the split-(110) interstitial sites was found. The results suggested that self-interstitial diffusion in Si occurred via diffusive jumps between the hexagonal sites and between hexagonal and split-(110) defects.

First-Principles Calculations of Self-Interstitial Defect Structures and Diffusion Paths in Silicon R.J.Needs: Journal of Physics - Condensed Matter, 1999, 11[50], 10437-50