Large-scale atomistic study of core structures and energetics of < c+a > {11(2)over-bar-2} dislocations in hexagonal close packed metals

Using two different kinds of many-body potentials as well as the Lennard-Jo nes potential for hexagonal close packed metals, we have found that (c + a) edge dislocations with dislocation lines along [1 (1) over bar 00] can spl it 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 struct ure has a large distorted region that we interpret as a (11 (2) over bar 1) twin nucleus, which may help the formation of (11 (2) over bar 1) tension twins. We also find that this core structure is lower in energy than the pr eviously observed glissile 'type II' configuration, dissociated on the (11 (2) over bar 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.