The dislocation core structure of self-interstitial atom (SIA) clusters in body-centered cubic iron and face-centered cubic copper was determined using the hybrid ab initio continuum method of Banerjee et al. (2007). To reduce reliance on empirical potentials and to facilitate predictions of the effects of local chemistry and stress on the structure of defects, a hybrid extension of the Peierls-Nabarro continuum model was presented here, with the lattice resistance to slip being determined separately from ab initio calculations. A method was developed to reconstruct atomic arrangements and geometry of SIA clusters from the hybrid model. The results were shown to compare well with molecular-dynamics simulations. In iron, the core structure does not show dependence on the size of the self-interstitial cluster, and was nearly identical to that of a straight edge dislocation. However, the core structure of SIA clusters in Cu was shown to depend strongly on the cluster size. Small SIA clusters were found to have non-dissociated compact dislocation cores, with a strong merging of Shockley partial dislocations and a relatively narrow stacking fault (SF) region. The compact nature of the SIA core in copper was attributed to the strong dependence of the self-energy on the cluster size. As the number of atoms in the SIA cluster increases, Shockley partial dislocations separate and the SF region widens, rendering the SIA core structure to that of an edge dislocation. The separation distance between thetwo partials widens as the cluster size increases, and tends to the value of a straight edge dislocation for cluster sizes above 400 atoms. The local stress was found to have a significant effect on the atomic arrangements within SIA clusters in copper and the width of the stacking faults. An applied external shear could delocalize the core of an SIA cluster in copper, with positive shear defined to be on the (111) plane along the [1̅ 1̅ 2] direction. For an SIA cluster containing 1600 atoms, a positive 1 GPa shear stress delocalizes the cluster and expands the SF to 30b, while a negative shear stress of 2 GPa contracts the core to less than 5b, where b was the Burgers vector magnitude

Structure of Self-Interstitial Atom Clusters in Iron and Copper. A.Takahashi, N.M.Ghoniem: Physical Review B, 80[17], 174104