Structures and electronic properties of small carbon nanotube tori

Fullerenes and nanotubes are promising candidates in the development of nan odevices. Recently, a form of carbon nanotube torus structures has been obs erved. In this regard, we have investigated the geometries, electronic stru ctures, and energetics of small carbon nanotube tori, using both the tight- binding and semiempirical quantum chemical approaches. It is shown that D-5 d nanotube tori behave like semiconductors, while D-6h nanotube tori exhibi t metal (or metal-like) characteristics similar to bent nanotubes. We show that the D-5d nanotube tori, which are as stable as the corresponding fulle renes, are energetically more favored than the corresponding nanotubes. In particular, the pentagons of the D-5d nanotube tori are less deformed than those of bent nanotubes and D-6h nanotube tori. This indicates that such sm all nanotube tori could be observed under optimal kinetic-driven conditions and eventually utilized as nanodevices.