The properties of large vacancy clusters, containing 10 to 40 vacancies, were investigated using an interatomic potential derived using the pseudopotential method. The stacking-fault energy of copper was calculated to be 65.3mJ/m2 for a potential cut-off radius of 8.5155Å; in good agreement with the experimental value of approximately 70mJ/m2. For larger cut-off radii, however, the calculated stacking energy decreased and became negative. It was suggested that this resulted from analytical fitting of the numerically calculated interatomic potential being inaccurate for relatively high interatomic radii. Using the a cut-off radius of 8.5155Å, the minimum energy configurations of hexagonal and triangular vacancy platelets of 10 or more vacancies were determined, and it was found that they collapsed into hexagonal faulted loops and stacking fault tetrahedra, respectively. This agreed with X-ray diffuse scattering experiments in which loops of this size were observed, and with previous calculations for copper using empirical interatomic potentials. The calculated displacement field at short distances above the small hexagonal loops differed significantly from linear isotropic inelasticity theory predictions. The stacking-fault tetrahedra were found to be more stable than hexagonal loops, although both were locally stable; in accord with experimental observations of both defects in copper.

Atomistic Simulation Study of Large Vacancy Clusters in Copper. M.J.Sabochick, S.Yip, N.Q.Lam: Journal of Physics F, 1988, 18[3], 349-61