Structures and electronic properties of small carbon nanotube tori

Fullerenes and nanotubes are promising candidates in the development of nanodevices. Recently, a form of carbon nanotube torus structures has been observed. In this regard, we have investigated the geometries, electronic structures, and energetics of small carbon nanotube tori, using both the tight-binding and semiempirical quantum chemical approaches. It is shown that ${D}_{5d}$ nanotube tori behave like semiconductors, while ${D}_{6h}$ nanotube tori exhibit metal (or metal-like) characteristics similar to bent nanotubes. We show that the ${D}_{5d}$ nanotube tori, which are as stable as the corresponding fullerenes, 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 small nanotube tori could be observed under optimal kinetic-driven conditions and eventually utilized as nanodevices.