Ground states of adsorbates on single-walled carbon nanotubes

We have investigated the ground states of single-walled carbon nanotubes with atoms adsorbed in the center of the hexagonal unit using the Monte Carlo method. We have determined the ground state structures of adsorbate on carbon nanotubes with different diameters. We have shown that the confinement has strong effects on the ground state structures. For the case of the zigzag $\mathrm{}(n,0\mathrm{})\mathrm{}$ nanotubes, when $n+1\mathrm{}$ can be divided exactly by 6, the ground state structures is the same as those of planar triangular lattice. Otherwise, novel ground state structures are found as a result of the size confinement of the system. We have also compared the results of zigzag type structures with those of armchair type. It is shown that the rolling way influences the ground state structures.