Structural model of semi-metallic carbon nanotubes



Electronic band structure and electronic density of states (DOS) of single-walled helically coiled carbon nanotubes (HCCNTs) are numerically calculated by symmetry implemented density functional tight binding method. It is found that unlike straight single-walled carbon nanotubes, single-walled HCCNTs can be semi-metallic, having high DOS at Fermi level. We show that this is a consequence of the local structure of HCCNTs, i.e., that by changing positions of pentagons and heptagons within a monomer, transitions between metallic, semi-metallic, quasi-metallic, and semiconducting structures can be made.