Lattice defects and boundaries in conducting carbon nanotubes

We consider the effect of various defects and boundary structures on the low-energy electronic properties in conducting zigzag and armchair carbon nanotubes. The tight-binding model of the conduction bands is mapped exactly onto simple lattice models consisting of two uncoupled parallel chains. Imperfections such as impurities, structural defects, or caps can be easily included into the effective lattice models, allowing a detailed physical interpretation of their consequences. The method is quite general and can be used to study a wide range of possible imperfections in carbon nanotubes. We obtain the electron-density patterns expected from a scanning tunneling microscopy experiment for half-fullerene caps and typical impurities in the bulk of a tube, namely, the Stone-Wales defect and a single vacancy.