  This study showed the structures and the thermal behaviors of Si nanocages
and nanotubes using classical molecular dynamics simulations based on the
Tersoff potential. For hypothetical Si nanotubes based on the Tersoff
potential, Si-Si bond length, cohesive energies per atom, diameters, and
elastic energy to curve the sheet into tube were in good agreement with those
obtained from previous density-functional theory results. Most of the
structures, which were obtained from the SA simulations for several initial
structures with diamond structure, have included encaged, tubular, or
sheet-like structures and have been composed of both sp3 and sp2 bonds. The
cohesive energies per atom for silicon nanotubes were higher than that for the
Si bulk in the diamond structure, and this implies the difficulty in producing
silicon nanotubes or graphitelike sheets. However, since the elastic energy per
atom to curve the sheet into tube for silicon atoms is very low, when
graphitelike sheets of silicon are formed, the extra cost to produce silicon
nanotubes is also very low. When silicon nanotubes are composed of both sp2 and
sp3 bonds and the ratio of sp3 to sp2 is high, since the probability of the
existence of silicon nanotubes increases, silicon nanotubes similar to multi
walled structures are anticipated.
