Bond lengths of armchair single-waled carbon nanotubes and their pressure dependence

We investigate the equilibrium structure of armchair single-wall carbon nanotubes at ambient conditions and under hydrostatic pressure. The structural parameters investigated are the bond lengths and bond angles. The bond lengths are determined for several radii tubes of various lengths. The procedure adopts generation of atomic coordinates based on the helical and rotational symmetries using two different bond lengths and then minimizing the energy to obtain best possible set of these bond lengths using Tersoff potential. Results show that one bond length is greater than that of the graphite while the other is smaller than that in graphite. The tube length is found to have significant effects on these bond lengths. These bonds were recalculated under hydrostatic pressure. The larger bond length decreases faster with pressure in comparison to the shorter one. As a result, at some critical pressure, depending upon the tube radius, these bond lengths match up each other before reversing their behavior above this critical pressure. It seems possible to uncover tube characteristics based on measurements having pressure dependence.