  Point defects in real crystals at finite temperatures are inevitable. Their
dynamics severely influence the mechanical properties of crystals under shear
giving rise to nonlinear effects such as ductility. Therefore, it is crucial to
explore the interplay of the equilibrium point-defect diffusion timescales and
shear-induced timescales to understand the plastic deformation of crystals.
Using extensive nonequilibrium molecular dynamics simulations, we present a
study on the yielding behavior of cluster crystals (CC), an archetypal model
for defect-rich crystals where the crystalline structure is characterized by
multiple occupancies (cluster) of particles at a lattice site. In equilibrium,
particles diffuse via site-to-site hopping keeping the crystalline structure
intact. We consider the CCs at a fixed density and different temperatures where
it remains in the FCC structure, and the diffusion timescales of particles vary
depending on the temperature. We choose the range of shear rates, which covers
timescales higher and much lower than the equilibrium diffusion timescales at
high temperatures. For the considered range of shear rates and temperatures,
both the macro and microscopic responses of CCs to the shear suggest that the
yielding scenario remains independent of the diffusion of particles. It
involves the plastic deformation of the underlying crystalline structure. The
averaged local bond order parameters and local angle measurements demonstrate
the structural changes and cooperative movement of the center of masses of the
clusters close to the yield point. A comparison with the soft-sphere (SS) FCC
crystal reveals the similarities in the yielding behavior of both systems.
Nonetheless, diffusion of particles influences certain features, such as a less
prominent increase in the local bond order parameters and local angles close to
the yield point.
