- The kinetics of cross-slip and annihilation of a screw dislocation dipole in face-centered cubic (FCC) copper crystals were studied by multiple molecular-dynamics simulations of long (200b) dislocations at selected stresses and temperatures with the aim to account for the thermally activated nature of the cross-slip process. A novel cross-slip mechanism was identified; this mechanism required the formation of a finite length constriction before cross- slip could be initiated. It was shown that point constrictions are not the transition state of cross-slip. A study of the kinetics confirmed that cross-slip is a first-order process. By fitting the rate constant to an Arrhenius form, the activation energy was found to be 1.05 eV±15%. The activation volume for the Escaig stress in the glide plane was in the range of 5–40b 3, and the prefactor for the rate constant was evaluated to be 1 THz/b.