On the importance of constrained atomic relaxations in the Nudged Elastic Band calculations of the Peierls barriers of dislocations

TL;DR

This paper shows that standard NEB calculations can misestimate Peierls barriers for dislocations in metals due to non-uniform dislocation distributions, and proposes a modified approach with constrained relaxations for more accurate results.

Contribution

The authors introduce a modified NEB method that applies relaxations only to dislocation position coordinates, improving the accuracy of Peierls barrier calculations in atomistic simulations.

Findings

Standard NEB overestimates Peierls barriers due to clustering effects.

Modified NEB with constrained relaxations yields more accurate Peierls stress values.

The new method aligns well with direct stress application results.

Abstract

We demonstrate that the straightforward application of the Nudged Elastic Band (NEB) method does not determine the correct Peierls barrier of 1/2<111> screw dislocations in BCC metals. Although this method guarantees that the states (images) of the system are distributed uniformly along the minimum energy path, it does not imply that the dislocation positions are distributed uniformly along this path. In fact, clustering of dislocation positions near potential minima occurs which leads to an overestimate of both the slope of the Peierls barrier and the Peierls stress. We propose a modification in which the NEB method is applied only to a small number of degrees of freedom that determine the position of the dislocation, while all other coordinates of atoms are relaxed by molecular statics as in any atomistic study. This modified NEB method with relaxations gives the Peierls barrier that increases smoothly with the dislocation position and the corresponding Peierls stress agrees well with that evaluated by the direct application of stress in the atomistic modeling of the dislocation glide.