Abstract
The properties of large vacancy clusters, containing from 10 to 40 vacancies, were investigated for copper using an interatomic potential derived from the pseudopotential method. The stacking fault energy of copper was calculated to be 65.3 mJ m-2 for a potential cut-off radius of 8.5155 AA, which is in good agreement with the experimental value of approximately 70 mJ m-2. For longer cut-off radii, however, the calculated stacking energy decreased and became negative. It is suggested that this results from the analytical fit of the numerically calculated interatomic potential being inaccurate at relatively long interatomic radii. Using the cut-off radius of 8.5155 AA, 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 agrees with X-ray diffuse scattering experiments in which loops of this size have been 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 the hexagonal loops, although both were locally stable, which is in accord with experimental observations of both defects in copper.