Assessment of interatomic potentials for atomistic analysis of static and dynamic properties of screw dislocations in W

TL;DR

This study evaluates five interatomic potentials for modeling screw dislocations in tungsten, analyzing their static and dynamic behaviors through atomistic simulations to identify the most accurate potential.

Contribution

It provides a comprehensive assessment of various potentials for simulating screw dislocations in W, highlighting the best compromise between accuracy and computational efficiency.

Findings

One potential predicts a core transformation affecting dislocation motion.

Most potentials show thermally-activated dislocation motion under stress.

The modified embedded-atom potential offers the best static and dynamic accuracy.

Abstract

Screw dislocations in bcc metals display non-planar cores at zero temperature which result in high lattice friction and thermally activated strain rate behavior. In bcc W, electronic structure molecular statics calculations reveal a compact, non-degenerate core with an associated Peierls stress between 1.7 and 2.8 GPa. However, a full picture of the dynamic behavior of dislocations can only be gained by using more efficient atomistic simulations based on semiempirical interatomic potentials. In this paper we assess the suitability of five different potentials in terms of static properties relevant to screw dislocations in pure W. As well, we perform molecular dynamics simulations of stress-assisted glide using all five potentials to study the dynamic behavior of screw dislocations under shear stress. Dislocations are seen to display thermally-activated motion in most of the applied stress range, with a gradual transition to a viscous damping regime at high stresses. We find that one potential predicts a core transformation from compact to dissociated at finite temperature that affects the energetics of kink-pair production and impacts the mechanism of motion. We conclude that a modified embedded-atom potential achieves the best compromise in terms of static and dynamic screw dislocation properties, although at an expense of about ten-fold compared to central potentials.