  We have performed atomistic simulations for helical multi-shell (HMS) Cu
nanowires and nanotubes. Our investigation on HMS Cu nanowires and nanotubes
has revealed some physical properties that were not dealt in previous works
that considered metal nanowires. As the diameter of HMS nanowires increased,
their cohesive energy per atom and optimum lattice constant decreased. As the
diameter of HMS nanotubes increases, their cohesive energy per atom decreased
but optimum lattice constant increased. Shell-shell or core-shell interactions
mainly affected on the lattice constant and the diameter of HMS nanowires or
nanotubes. This study showed that HMS nanotubes for materials of fcc metal
crystals can be maintained when forces exerted on atoms of inner shell of the
HMS nanotubes are zero or act on the direction of the outside.
