Understanding the thermally activated glide of dislocations from the atomic scale

David Rodney
Institut National Polytechnique de Grenoble (INPG)

Depending on their core structure, dislocations can be subjected to a high lattice friction, leading to a strong effect of thermal activation at low temperatures. Probably the best-known example is the screw dislocation in BCC crystals. Molecular Dynamics (MD) is not well adapted to simulate dislocation glide in the thermally-activated regime due to the strong limitation in timescale accessible to dynamical simulations. We show here that a static approach, combining saddle-point search methods (the Activation-Relaxation Technique and Nudged Elastic Band method) to identify energy pathways and the Transition State Theory (TST) to predict kinetics, allows understanding and modeling accurately the thermally-activated glide of dislocations. We will show how the Peierls potential, accounting for its stress dependence, can be computed and used in a line tension model to predict the kink-pair formation enthalpy, from which dislocation kinetics at high temperature in the classical regime can be deduced and compared to direct MD simulations. At low temperature, we will show that zero-point quantum corrections to include quantum statistics in the vibrational modes of the crystal, must be introduced in the TST to predict accurately dislocation kinetics and in particular, not to overestimate the Peierls stress in the limit of zero temperature, as reported recently in Proville, Rodney, Marinica, Nature Materials, doi: 10.1038/nmat3401 (2012).

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