On the significance of model design in atomistic calculations of the Peierls stress in Nb

WR Jian and SZ Xu and IJ Beyerlein, COMPUTATIONAL MATERIALS SCIENCE, 188, 110150 (2021).

DOI: 10.1016/j.commatsci.2020.110150

The Peierls stress required for a single dislocation to glide in a perfect crystal is considered one of the most important properties controlling plastic deformation of metals. Values for the Peierls stress computed by atomistic models often differ even for the same dislocation and when using the same material interatomic potential, limiting their value in understanding material behavior. Here, using molecular static simulations, we study the effects of model configuration, model size, and loading mode on the Peierls stress of an edge dislocation on the 112 glide plane in body-centered cubic Nb in the twinning and anti- twinning senses of slip. The analysis includes six model configurations, a model size range spanning over an order of magnitude, and three loading modes, all repeated for two interatomic potentials for Nb. Results show that, in most cases studied, smaller model sizes artificially lead to lower Peierls stresses. The study also reveals a substantial effect of model configuration on whether the Peierls stress converges with size, the minimum size required for convergence, and the magnitude of the Peierls stress. Only one model configuration, the periodic array of dislocation (PAD) model, achieves a strictly converged value for the two interatomic potentials considered here. In addition, PAD model predicts the lowest Peierls stress values among all model configurations, provided that the model size is sufficiently large. We show that with the same interatomic potential, while one model configuration predicts a higher anti-twinning Peierls stress than twinning Peierls stress, another one may predict the opposite asymmetry. Unlike the stress-controlled loading mode, the shear-controlled and displacement-controlled loading modes provide similar results using both potentials. The findings here will be useful for selecting the appropriate model settings in research studies involving Peierls stress calculations via atomistic simulations.

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