Nudged elastic band calculations of stacking and dislocation pathways in diamond

TL;DR

This study uses ab initio calculations and the Nudged Elastic Band method to map stacking fault energy landscapes in diamond, revealing lower energy barriers and more realistic curved pathways than previous linear models, enhancing understanding of diamond's plasticity.

Contribution

It introduces a NEB-based approach to determine minimum energy paths for stacking and dislocation in diamond, considering transverse slip plane freedom, which was neglected in prior studies.

Findings

Stacking energy barriers are significantly lower than previously reported.

Curved pathways on the slip plane have lower energy barriers than straight-line models.

The glide-set exhibits a lower energy barrier than the shuffle-set across the entire stacking plane.

Abstract

Diamond, the hardest natural crystal, has attracted significant attention for its plasticity, which is reported to be determined by its stacking faults. Studies mainly focused on one-dimensional linear pathways in stacking transitions, neglecting its transverse freedom on the main slip plane. However, in an actual stacking procedure, stacking faults can follow curve line along the slip plane rather than constrained to straight lines. In this study, using ab initio calculations, we mapped the {\gamma}-surface, defined as the landscape of generalized stacking fault energies, along the weakest direction of the {111} orientation in diamond. We then applied the Nudged Elastic Band (NEB) method to determine the minimum energy paths, finding significantly reduced stacking energy barriers compared to previous reports (for the glide-set, our energy barrier is only one-third of that for the traditional direct path). Our calculations reveal that the glide-set can round its high-energy peak, with a lower energy barrier within the entire stacking plane than the shuffle-set. By employing the NEB method, we have constructed the minimum energy path (MEP) for both the stacking and dislocation procedures. Our results provide new insights into the plasticity and stacking faults of diamond, advancing the understanding of superhard carbon material transition, especially the diamond under shear stress.