Plastic deformation in metals is controlled by dislocation density and mobility. In bcc metals the mobility of screw dislocations, which takes place by temperature- and stress-driven nucleation of critical kink-pairs, is most essential for deformation. However, the critical resolved shear stresses at low temperatures, as determined from molecular dynamics (MD) simulations performed at constant strain rate, are typically 2–3 times larger than the yield stresses measured experimentally. Here, an accelerated MD procedure is developed and employed to investigate the onset of dislocation mobility in the prototypical system bcc Nb. The method combines constant strain and temperature MD with hyperdynamics, using a bond-boost potential. We demonstrate, with a careful statistical analysis, that the method enables nucleation of critical kink-pairs and the determination of the Gibbs energy of kink-pair formation from accelerated MD simulations at experimentally-measured shear stresses.

金属的塑性变形受位错密度和迁移率的控制。在 bcc 金属中，螺旋位错的迁移率是由温度和应力驱动的临界扭结对成核发生的，对于变形是最重要的。然而，根据在恒定应变速率下进行的分子动力学 (MD) 模拟确定的低温下临界解析剪切应力通常比实验测量的屈服应力大 2-3 倍。在这里，开发了一种加速的 MD 程序并用于调查发病原型系统 bcc Nb 中的位错迁移率。该方法使用键增强电位将恒定应变和温度 MD 与超动力学相结合。我们通过仔细的统计分析证明，该方法能够使临界扭结对成核，并在实验测量的剪切应力下通过加速 MD 模拟确定扭结对形成的吉布斯能量。