Large-scale atomistic study of core structures and energetics of (()) dislocations in hexagonal close packed metals

Using two different kinds of many-body potentials as well as the Lennard-Jones potential for hexagonal close packed metals, we have found that c + a edge dislocations with dislocation lines along 1 00 can split onto the basal plane, forming a non-planar sessile structure. The `type I' undissociated dislocation core, observed in previous papers, is shown to be stable only for small simulations. The observed dissociated core structure has a large distorted region that we interpret as a (11 1) twin nucleus, which may help the formation of (11 1) tension twins. We also find that this core structure is lower in energy than the previously observed glissile `type II' configuration, dissociated on the (11 2) plane. The sessile splitting of the core gives rise to non-Schmid behaviour, with the twin nucleus expanding under c -axis tension, and contracting under compression.