Determination of positions and curved transition pathways of screw dislocations in BCC crystals from atomic displacements

The theoretical description of the thermally activated dislocation glide in pure crystals depends crucially on the shape of the Peierls barrier that the dislocation has to overcome when moving through the lattice. While the height of this barrier can be obtained using saddle-point search algorithms such as the Nudged Elastic Band (NEB) method, its exact shape depends on the details of the approximation of the transition pathway of the system. The purpose of this paper is to formulate a procedure that allows to identify the dislocation positions along the path directly from the displacements of atoms in its core. We investigate the performance of this model by calculating curved paths of the 1/2[111]1/2[111] screw dislocation in tungsten modeled by a Bond Order Potential using a series of images obtained by employing a modified NEB method at zero applied stress and for positive/negative shear stresses perpendicular to the slip direction. The Peierls barriers resulting from the curved paths are shown to be substantially different from those obtained when assuming straight dislocation path. For both straight and curved dislocation pathways we calculate the temperature dependencies of the flow stress and compare these predictions with direct experimental measurements. We show that a significantly better agreement with experiments is obtained if the curved dislocation pathway is taken into account.