Electronic structure calculations were used to study the relaxation, formation and binding energies of small He clusters in Fe. Three He defect configurations were considered: two He atoms in an interstitial position and two and three He atoms located in one vacancy. In order to study He–vacancy clusters containing more He atoms, a multi-scale approach was used and an empirical potential was fitted to both the formation and relaxation energies of a single He defect and small He clusters obtained from first-principles calculations. The potential consisted of a repulsive pair-interaction part and a many-body attractive term which described the cohesion. The potential was used to study stability of He-vacancy clusters at zero temperature. The binding energy of a He atom to a He-cluster varies from 1.3 to 1.9eV; depending upon the cluster size. When more than six He atoms were placed into a vacancy an Fe self-interstitial atom was produced. The self-interstitial atom binding energy to a He–di-vacancy cluster decreased from 5.0 to 0.7eV as the number of He atoms increased. The results obtained were consistent with reported experimental observations of He desorption.

Calculation of Helium Defect Clustering Properties in Iron using a Multi-Scale Approach. T.Seletskaia, Y.N.Osetsky, R.E.Stoller, G.M.Stocks: Journal of Nuclear Materials, 2006, 351[1-3], 109-18