Self-interstitials in V and Mo

We report an extensive ab initio study of self-interstitials in V and Mo. Contrary to the widely accepted picture, the 〈111〉 dumbbell is found to be the most stable structure. The activated state for migration is the crowdion configuration, with an extremely low barrier (∼0.01 eV), suggesting 1d (one-dimensional) diffusion at low temperatures and 3d diffusion at high temperature. In the case of Mo, the energy landscape between the 〈111〉 and 〈110〉 dumbbells is very shallow. Predicted migration energies and self-interstitial structures are consistent with experiment.