  Atomistic simulations are performed to probe the anisotropic deformation in
the compressions of face-centred-cubic metallic nanoparticles. In the elastic
regime, the compressive load-depth behaviors can be characterized by the
classical Hertzian model or flat punch model, depending on the surface
configuration beneath indenter. On the onset of plasticity, atomic-scale
surface steps serve as the source of heterogeneous dislocation in nanoparticle,
which is distinct from indenting bulk materials. Under [111] compression, the
gliding of jogged dislocation takes over the dominant plastic deformation. The
plasticity is governed by nucleation and exhaustion of extended dislocation
ribbons in [110] compression. Twin boundary migration mainly sustain the
plastic deformation under [112] compression. This study is helpful to extract
the mechanical properties of metallic nanoparticles and understand their
anisotropic deformation behaviors.
