Vacancy loops and stacking-fault tetrahedra in copper - I. Structure and properties studied by pair and many-body potentials

The structure and properties of vacancy loops (VIs) and stacking-fault tetr ahedra (SFTs) in copper have been studied by computer simulation using a lo ng-range pair interatomic potential (LRPP), obtained from the generalized p seudopotential theory, and a many-body potential (MBP) of Finnis-Sinclair t ype. The results obtained for these different potentials are qualitatively different. Thus, for the LRPP, significant atomic relaxation is observed fo r all defects. Triangular vacancy platelets relax into regular SFTs, and sm all hexagonal clusters form Frank loops, whereas large hexagonal clusters ( containing more than 37 vacancies) can dissociate into six truncated SFTs w ith the side equal to the [110] side of the hexagon. Similar features are o bserved after the relaxation of circular loops. For the MBP, on the other h and, none of the hexagonal, circular and triangular planar vacancy platelet s relax into a VL or SFT but remain almost unrelaxed 'holes', with a relati ve stability which is weakly dependent on the shape. The results obtained a re compared with experiment and the results of other computer simulations, and the differences stemming from the use of different interatomic potentia ls and different simulation methods are discussed.