  It is now possible to create perfect crystal nanowires of many metals. The
deformation of such objects requires a good understanding of the processes
involved in plasticity at the nanoscale. Isotropic compression of such
nanometre scale micropillars is a good model system to understand the
plasticity. Here we investigate these phenomena using Molecular Dynamics (MD)
simulations of nanometre scale single crystal BCC iron pillars in compression.
  We find that pillars with large length to width ratio may buckle under high
strain rates. The type of buckling behaviour depends sensitively on the
boundary conditions used: periodic boundary conditions allow for rotation at
top and bottom of the pillar, and result in an S shaped buckle, by contrast
fixed boundaries enforce a C shape. Pillars with a length to width ratio closer
to that used in experimental micropillar compression studies show deformation
behaviour dominated by slip, in agreement with the experiments. For
micropillars oriented along <100>, slip occurs on <110> planes and localized
slip bands are formed. Pillars of this size experience higher stresses than
bulk materials before yielding takes place. One might expect that this may be
in part due to the lack of nucleation sites needed to induce slip. However,
further simulations with possible dislocation sources: a shorter iron pillar
containing a spherical grain boundary, and a similar pillar containing jagged
edges did not show a decreased yield strength.
