Coupled-barrier diffusion: The case of oxygen in silicon

Oxygen migration in silicon corresponds to an apparently simple jump between neighboring bridge sites. Yet extensive theoretical calculations have so far produced conflicting results and have failed to provide a satisfactory account of the observed 2.5 eV activation energy. We report a comprehensive set of first-principles calculations that demonstrate that the seemingly simple oxygen jump is actually a complex process involving coupled barriers and can be properly described quantitatively in terms of an energy hypersurface with a ''saddle ridge'' and an activation energy of similar to 2.5 eV. Earlier calculations correspond to different points or lines on this hypersurface.