Structural Trends Interpretation of the Metal-to-Semiconductor   Transition in Deformed Carbon Nanotubes
  Two mechanisms that drive metal-to-semiconductor transitions in single-walled carbon nanotubes are theoretically analyzed through a simple tight-binding model. By considering simple structural trends, the results demonstrate that metal-to-semiconductor transitions can be induced more readily in metallic zigzag nanotubes than in armchair nanotubes. Furthermore, it is shown that both mechanisms have the effect of making the two originally equivalent sublattices physically distinguishable. 
Jun-Qiang Lu, Jian Wu, Wenhui Duan, Bing-Lin Gu, H.T. Johnson