  The kinetics of dislocation reactions, such as dislocation multiplication,
controls the plastic deformation in crystals beyond their elastic limit,
therefore critical mechanisms in a number of applications in materials science.
We present a series of large-scale molecular dynamics simulations that shows
that one such type of reactions, the nucleation of dislocation at free
surfaces, exhibit extremely unconventional kinetics, including unexpectedly
large nucleation rates under compression, very strong entropic stabilization
under tension, as well as strong non-Arrhenius behavior. These unusual kinetics
are quantitatively rationalized using a variational transition state theory
approach coupled with an efficient numerical scheme for the estimation of
vibrational entropy changes. These results highlight the need for a variational
treatment of the kinetics to quantitatively capture dislocation reaction
kinetics, especially at low-to-moderate strains where large deformations are
required to activate reactions. These observations suggest possible
explanations to previously observed unconventional deformation kinetics in both
molecular dynamics simulations and experiments.
