  Molecular dynamics simulations revealed significant difference in deformation
behaviour of $<$100$>$ BCC Fe nanowires with and without twist boundary. The
plastic deformation in perfect $<$100$>$ BCC Fe nanowire was dominated by
twinning and reorientation to $<$110$>$ followed by further deformation by slip
mode. On the contrary, $<$100$>$ BCC Fe nanowire with a twist boundary deformed
by slip at low plastic strains followed by twinning at high strains and absence
of full reorientation. The results suggest that the deformation in $<$100$>$
BCC Fe nanowire by dislocation slip is preferred over twinning in the presence
of initial dislocations or dislocation networks. The results also explain the
absence of extensive twinning in bulk materials, which inherently contains
large number of dislocations.
