Theoretical study of the effect of point defects on the elastic constants of copper

Using the recently published semi-empirical potential of Ackland, Tichy, Vitek and Finnis for copper, and a standard Morse potential, the change in elastic constants due to the introduction of self-interstitial atoms (SIAs) and vacancies into a perfect lattice is investigated. Elastic energy is calculated for various strained states, using the technique of quenched molecular dynamics. The relaxed configuration of these strained states is thus found and the elastic constants are calculated from the energies of these strained states. Constant pressure molecular dynamics is used to find the fully relaxed position of the <100> SIA and that of the vacancy in an unstrained case. From this unstrained configuration the dipole tensor (Pij) is calculated, and from the change in elastic moduli the polarisabilities (αijkl) are calculated. The dipole tensor is found to be qualitatively similar with both potentials, but differences in sign are found in the polarisabilities. Isolated interstitials are found to increase all the elastic moduli, contrary to previous calculations, whereas their mutual interaction tends to reduce the moduli. In conjunction with experimental data, this work provides evidence for the formation of clusters of interstitials, and suggests that the SIPA model of irradiation creep is not applicable to copper. (orig.)