**Screw dislocation structure and mobility in body centered cubic Fe
predicted by a Gaussian Approximation Potential**

F Maresca and D Dragoni and G Csanyi and N Marzari and WA Curtin, NPJ COMPUTATIONAL MATERIALS, 4, 69 (2018).

DOI: 10.1038/s41524-018-0125-4

The plastic flow behavior of bcc transition metals up to moderate
temperatures is dominated by the thermally activated glide of screw
dislocations, which in turn is determined by the atomic-scale screw
dislocation core structure and the associated kink-pair nucleation
mechanism for glide. Modeling complex plasticity phenomena requires the
simulation of many atoms and interacting dislocations and defects. These
sizes are beyond the scope of first-principles methods and thus require
empirical interatomic potentials. Especially for the technological
important case of bcc Fe, existing empirical interatomic potentials
yield spurious behavior. Here, the structure and motion of the screw
dislocations in Fe are studied using a new Gaussian Approximation
Potential (GAP) for bcc Fe, which has been shown to reproduce the
potential energy surface predicted by density-functional theory (DFT)
and many associated properties. The Fe GAP predicts a compact, non-
degenerate core structure, a single-hump Peierls potential, and glide on
*110*, consistent with DFT results. The thermally activated motion at
finite temperatures occurs by the expected kink-pair nucleation and
propagation mechanism. The stress-dependent enthalpy barrier for screw
motion, computed using the nudgedelastic- band method, follows closely a
form predicted by standard theories with a zero-stress barrier of
similar to 1 eV, close to the experimental value of 0.84 eV, and a
Peierls stress of similar to 2 GPa consistent with DFT predictions of
the Peierls potential.

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