First-principles methods were used to calculate the structures and local vibrational modes of interstitial O pairs. The staggered Oi-Si-Oi and skewed Oi-Si-Si-Oi structures were nearly degenerate in energy. The calculated local vibration frequencies and their pure and mixed 18O → 16O isotopic shifts agreed closely with experiment. The highest frequency was attributed to the skewed structure, and the 4 lower ones were attributed to the staggered structure. This was expected to resolve the controversy concerning O dimers in Si, as well as suggesting a mechanism for fast O diffusion.

Vibrations of Interstitial Oxygen Pairs in Silicon M.Pesola, I.Von Boehm, R.M.Nieminen: Physical Review Letters, 1999, 82[20], 4022-5