Density-functional theory studies of step-kinked carbon nanotubes

Using density-functional theory (DFT) methods, we investigate structural, electronic, and transport properties of step-kinked single-walled carbon nanotubes (SWCNT). To devise a sensible model for the joint section of the kinked nanotube, we examine relative stability of two (6,0) carbon-nanotube- based C₆₇₂ isomers, namely, a carbon nanoring and a carbon hexagonal nanotorus. We find that the hexagonal nanotorus C₆₇₂ is energetically more favorable than the isomeric nanoring (i.e., circular nanotorus) C ₆₇₂. By use of the kinked section of the hexagonal nanotorus as a model joint, the periodic step-kinked carbon nanotubes can be built. According to the DFT calculation using the hybrid B3LYP functional, we find that introduction of the periodic kinks turns the perfect (5,0) SWCNT with zero band gap (J. Phys. Chem. Lett. 2010, 1, 2946) into a semiconductor with a band gap ∼0.76 eV. In contrast, the step-kinked (6,0) SWCNT is still a metal with zero band gap, like the perfect (6,0) SWCNT. We also compare the electronic transport properties of a perfect (5,0) SWCNT with the step-kinked (5,0) SWCNT. The former has a nonzero steplike electron transmission distribution near the Fermi level, while the latter shows some sharp transmission peaks around the Fermi level.