Complex evolution of dislocation core structure in a process of motion: Model analysis with ab-initio parameterization

We extend the Peierls-Nabarro (PN) model to eliminate the "continuum" approximation for the misfit energy, and use it to analyze features of the evolution of the dislocation core structure under various stress conditions (glide and Escaig stress). We show that the core may assume competing multiple structures with their marked dependence on the dislocation axis position. As we demonstrate for ordinary dislocations in fee Ir and the ordered L1_o CuAu calculated using ab-initio generalized stacking fault energies, these lattice discreteness effects, missing in the original PN model, significantly affects the evolution of the dislocation under stress. In particular, these effects may result in the ladder-like dependence of the partial separation under Escaig stress conditions, and dramatic changes in the shape and amplitude of the Peierls barrier. Thus, we find that lattice discreteness effects can be significant not only in ordered alloys with a deep Peierls valley but also in fee metals under stress and further, these effects result in the evolution of dislocation structure which is more complex than previously thought.