Abstract Submitted to the    NANOTUBE'04 Conference:

Spin-polarized density functional theory is used to calculate the properties of vacancies in a graphene sheet and in single-walled carbon nanotubes (SWNTs). For graphene, we find that vacancies are magnetic, and that the symmetry of the sheet is broken by a distortion of an atom next to the vacancy site. We also study vacancies in four armchair SWNTs from (3, 3) to (6, 6) and six zigzag SWNTs from (5, 0) to (10, 0). The calculations demonstrate that vacancies can change the electronic structure of the SWNTs, converting some metallic nanotubes to semiconductors and some semiconducting nanotubes to metals. The metallic nanotubes with vacancies exhibit ferromagnetism or ferrimagnetism, while some semiconducting nanotubes with vacancies show antiferromagnetic order. The magnetic properties depend on the chiralities of the tubes, the configuration of the vacancy and the concentration of the vacancies.