In body-centred-cubic (bcc) metals migrating 1/2<111> screw dislocations experience a periodic energy landscape with a triangular symmetry. Atomistic simulations, such as those performed using the nudged-elastic-band (NEB) method, generally predict a transition-pathway energy-barrier with a double-hump; contradicting Ab Initio findings. Examining the trajectories predicted by NEB for a particle in a Peierls energy landscape representative of that obtained for a screw dislocation, reveals an unphysical anomaly caused by the occurrence of monkey saddles in the landscape. The implications for motion of screws with and without stress are discussed.
@article{arxiv.1307.3848,
title = {Degenerate transition pathways for screw dislocations: implications for migration},
author = {Mark R. Gilbert and Sergei L. Dudarev and Peter M. Derlet},
journal= {arXiv preprint arXiv:1307.3848},
year = {2013}
}