Nature of single vacancy in achiral carbon nanotubes.

We have performed systematic calculations for single vacancies and their related point defects in achiral carbon nanotubes using a tight-binding model. Our calculations clarify that the local structures around single vacancies in such tubes do reconstruct with no constraint. We find that the structural configuration and formation energy of the resulting point defect are dependent on the radius and chirality, as well as the electric properties of a tube. The electronic structures of the single vacancies also depend strongly upon the chirality of the carbon nanotubes.