First-principles density functional calculations, using Gaussian orbitals, were carried out on large super-cells which contained O defects. The formation energies, local vibrational modes and diffusion or reorientation energies of Oi, O2i, VO, VOH and VO2 were investigated. The piezospectroscopic tensors for Oi, VO and VO2 were also evaluated. The vibrational modes of Oi were consistent with the view that the defect effectively had D3d symmetry under low hydrostatic pressures, but adopted a buckled structure under high pressures. An anomalous temperature dependence of the modes of O2i was attributed to an increased buckling of Si-O-Si when the lattice contracted. The diffusion energy of the dimer was about 0.8eV lower than that of Oi. The dimer was stable with respect to VO or VO2 formation, and the latter defect had modes which were close to the reported 894/cm band. The reorientation energies of O and H in VO and VOH defects were found to be equal to a few tenths of an eV, and were greater when the defect trapped an electron.

Oxygen and Di-Oxygen Centres in Si and Ge: Density-Functional Calculations. J.Coutinho, R.Jones, P.R.Briddon, S.Oberg: Physical Review B, 2000, 62[16], 10824-40