Stability and mobility of self-interstitials and small interstitial clusters in α-iron: ab initio and empirical potential calculations

The stability and mobility of self-interstitials and small interstitial clusters, In, in α-Fe is investigated by means of calculations performed in the framework of the density functional theory using the SIESTA code. The mono-, di- and tri-interstitials are shown to be made of (parallel) 〈1 1 0〉 dumbbells and to migrate by nearest-neighbor translation-rotation jumps, according to Johnson's mechanism. The 〈1 1 1〉 orientation of the dumbbells becomes energetically more favourable for I5 and larger clusters. The performance of a semi-empirical potential recently developed for Fe, including ab initio self-interstitial data in the fitted properties, is evaluated over the present results. The superiority over previous semi-empirical potentials is confirmed. Finally the impact of the present results on the formation mechanism of 〈1 0 0〉 loops, observed experimentally in α-Fe is discussed.