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

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.