Abstract
The stability of various atomic configurations for an interstitial is investigated in a model representing copper. For the interaction between the lattice ions, a Born-Mayer and a Morse potential are used. Two equilibrium configurations are found for an interstitial. For the two stable positions the formation energies and the changes in volume of the crystal arising from the interstitial are calculated. The calculations show that the crowdion and the "body-centered" interstitial are unstable.