Deformation modes of diamond using first-principles calculations: Uniform versus local deformation

T Fu and CY Li and H Hu and MY Duan and SY Weng and XH Peng, DIAMOND AND RELATED MATERIALS, 160, 113040 (2025).

DOI: 10.1016/j.diamond.2025.113040

Recent advances in microstructural design, such as nanotwinned and hierarchical structures, have significantly enhanced the hardness and toughness of diamond. However, first-principles calculations often predict global graphitization under tension and under shear, contradicting localized deformation observed in experiments. This discrepancy arises from the strict symmetry constraints conventionally imposed in these calculations, which oversimplify the deformation behavior. By breaking such symmetry constraints, we revealed a transition from global graphitization to localized fracture in single- crystal diamond under tension and to localized partial slip under shear. The comparative study for FCC Cu further supports our findings, showing similar transitions from uniform deformation to localized partial slips. Additionally, ab initio molecular dynamics simulations demonstrated that, at finite temperatures, localized failure dominates the deformation of diamond, with critical strains and peak stresses lower than those predicted by conventional methods. These results highlight the limitations of symmetry-based approaches in capturing the realistic deformation behavior and challenge the existing strengthening mechanisms based on graphitization. This study can provide a new framework for investigating the deformation modes and ideal strengths of crystalline materials using first-principles calculations.

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