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Accelerated molecular dynamics reveals a mechanism transition and strong temperature dependence of dislocation nucleation from grain boundaries (GBs) in Cu. At stress levels up to $\ensuremath{\sim}90%$ of the ideal dislocation-nucleation stress, atomic shuffling at the $E$ structural unit in a GB acts as a precursor to dislocation nucleation, and eventually a single dislocation is nucleated. At very high stress levels near the ideal dislocation-nucleation stress, a multiple dislocation is collectively nucleated. In these processes, the activation free energy and activation volume depend strongly on temperature. The strain-rate dependence of the critical nucleation stress is studied and the result shows that the mechanism transition from the shuffling-assisted dislocation-nucleation mechanism to the collective dislocation-nucleation mechanism occurs during the strain rate increasing from ${10}^{\ensuremath{-}4}\phantom{\rule{0.16em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}\mathrm{to}\phantom{\rule{0.16em}{0ex}}{10}^{10}\phantom{\rule{0.16em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$.

Mechanism transition and strong temperature dependence of dislocation nucleation from grain boundaries: An accelerated molecular dynamics study