It was recalled that the Peierls-Nabarro model had originally been developed in order to describe core spreading on the slip plane of a dislocation. It was noted that screw dislocations had more than one slip plane and were expected to dissociate in a non-planar fashion which reflected the symmetry about the screw axis. The Peierls-Nabarro model was here generalized in order to account for non-planar core spreading. A symmetrical mode of dissociation was considered as an illustration of the possibilities of the new approach. Real screw cores were not expected to be symmetrical, as such an arrangement might not be stable. Other problems which might be treated included estimations of the Peierls stress and of the recombination energy for dislocation motion. It was concluded that the Foreman theorem, that the fault energy was invariant in the original Peierls-Nabarro model, also needed to be re-assessed.

On Generalizing the Peierls-Nabarro Model for Screw Dislocations with Non-Planar Cores. A.H.W.Ngan: Philosophical Magazine Letters, 1995, 72[4], 207-13