Dependence of In-Tube Carbon Chain on the Radius and Helicityof Single-Wall Carbon Nanotubes

Using the Lennard-Jones interaction potential, we have studied the in-tube carbon-chain structure doped into the single-wall carbon nanotubes (SWCNTs). Through minimizing the potential energy of the doped system, it is found that the optimal structure of the doping carbon chain is spiral, but not a straight line, when the radius of the SWCNT is larger than about 4.30Å.