The deposition of energetic Cu atoms from 5 to 80 eV onto (0 0 1) Cu was simulated with molecular dynamics. The Cu-Cu interaction potential was a spline of the embedded atom potential developed from equilibrium data, and the universal scattering potential. Incident Cu atoms substituted for first layer substrate atoms by an exchange process at energies,is low as 5 eV. Incident Cu atoms of 20 eV penetrated to the second substrate layer, and 20 eV was sufficient energy to produce interstitial defects. Incident atoms of 80 eV penetrated to the third atomic layer, produced interstitials 12 atomic layers into the substrate by focused replacement collision sequences, and produced sputtered atoms with a 16% yield. Interstitial clusters of up to 7 atoms were observed. The observed mechanisms of film growth included: the direct deposition of atoms into film equilibrium atom positions., the exchange of substrate atoms to equilibrium film atoms positions, and the migration of interstitials to equilibrium film atom positions. The relative frequency of each process was a function of incident ener-. Since all observed growth Mechanisms resulted in film atoms in equilibrium atomic positions, these simulations suggest that,tresses in homoepitaxial Cu thin films are due to point defects. Vacancies would produce tensile strain and interstitial atom,, would produce compressive strain in the films. It is proposed that immobile interstitial clusters could be responsible for retaining interstitial atoms and dusters in growing metal thin films.