Formation energetics of n-member rings at the end of small zigzag carbon nanotubes

The formation energetics and stability of n-member rings at the end of small zigzag carbon nanotubes are investigated using k-space tight-binding molecular dynamics simulations (TBMDs). It is found that at 1100 °C the initial dangling atoms at the end of a small (n,0) zigzag carbon nanotube can transform into an n-member ring if the tube is larger than a (3,0) tube but smaller than a (11,0) tube. For zigzag tubes larger than (10,0) the large strain associated with the n-member ring prevents the formation of the ring at the end of the tube. It is shown that the 6-member ring formed at the top of a (6,0) tube is the most stable one, and that the formation of the ring at the top of small zigzag tubes may introduce new ring states around the Fermi level.