Bond alternation in carbon nanotubes including σ-electrons

We have examined the bond-alternation patterns of the energetically optimized structures of single-layer carbon nanotubes predicted to be "metallic" by the earlier Hückel-type treatment in order to check the possibility of Peierls distortion. A semiempirical one-dimensional tight-binding crystal orbital (1D-TBCO) method including all the valence electrons was employed in the calculation. It was found that a certain bond alternation appears in the "metallic" tubes but that such alternation does not necessarily cause a breakdown of the metallic band structure.