Vacancy and Cu-vacancy clusters in body-centered cubic Fe-Cu alloys were studied using a combination of metropolis Monte Carlo and molecular dynamics techniques, to investigate their lowest energy configurations and corresponding binding energies, for sizes up to a few hundreds of elements (about 2nm). Two different many-body interatomic potentials were used to perform the calculations, in order to assess the robustness of the results. Empirical expressions for the binding energies, of immediate use in kinetic Monte Carlo or rate-theory models, were obtained. It was observed that vacancy clusters were three-dimensional cavities whose shape was primarily determined by a criterion of maximization of the number of first and second nearest neighbor pairs. Copper atoms, when present, tend to coat an inner vacancy cluster, while remaining first nearest neighbors to each other. The inner vacancy cluster, when completely coated, tends to be as close as possible to the surface of the hollow precipitate. These findings were consistent with previous experimental and computational work. The binding energy of these complexes was a monotonously growing function of the ratio number of vacancies to number of Cu atoms. Pure Cu precipitates appeared to follow a loose criterion of maximization of first nearest neighbor pairs. While the 2 interatomic potentials used here provided largely similar values for the binding energies and comparable configurations, some differences were found.

On the Binding Energies and Configurations of Vacancy and Copper-Vacancy Clusters in BCC Fe-Cu - a Computational Study. D.Kulikov, L.Malerba, M.Hou: Philosophical Magazine, 2006, 86[2], 141-72