Structure and energetics of hydrogenated and dehydrogenated carbon tori

It is shown that large-diameter, finite and extended, hydrogenated, single-walled carbon nanotubes are energetically and structurally unstable. The instability of short, large-diameter, finite hydrogenated tubes leads to the formation of hydrogenated circular carbon tori of small tubular cross-section. It is also shown that carbon toroidal structures, formed by desorption of hydrogen from the hydrogenated tori, are more energetically stable than the corresponding open-ended, finite single-walled carbon nanotubes.