Controlling screw dislocation core structure and Peierls barrier in BCC interatomic potentials

Abstract

For screw dislocations in BCC metals, three mysteries have persisted, that is, compact vs degenerate core structure, single-hump vs double-hump Peierls barrier, and the relation between the core structure and Peierls barrier. We discover that the compact core consists of atoms in a FCC stacking sequence and that the degenerate core consists of atoms in a HCP stacking sequence, suggesting that BCC, FCC, and HCP must be considered to correctly capture the core structure. Informed by a machine learning model, we can generate interatomic potentials that reliably predict a compact core structure. We further show the compact core structure does not necessarily lead to the single-hump Peierls barrier.