Molecular statics and molecular dynamics simulation methods were used to study the structural relaxation of small (less than 10) vacancy and interstitial clusters. It was found that vacancy clusters whose size was less than 4 did not relax much, whereas clusters which were larger than 5 relaxed appreciably; often into a stacking-fault tetrahedron and an octahedral void. It was noted that the stacking-fault tetrahedra of hexa-vacancies relaxed into a void. Interstitials were introduced into body-centered cubic positions. A di-interstitial was found to relax into 2 parallel <110> split interstitials, and tri- or tetra-interstitials relaxed to composite clusters of <100> split interstitials and a body-centered cubic interstitial. Penta- or hexa-interstitials formed agglomerates of parallel <110> crowdions whose central portions were not on a single (111) plane. Such structures permitted the easy motion of these clusters along <110> directions under stress. It was recalled that movements of interstitial clusters had been observed in neutron-irradiated Au and Cu.

Y.Shimomura, R.Nishiguchi, T.Diaz de la Rubia, M.W.Guinan: Radiation Effects and Defects in Solids, 1994, 129[1-2], 81-9