  Fundamentally new families of carbon single walled nanotubes are proposed.
These nanotubes, called graphynes, result from the elongation of covalent
interconnections of graphite-based nanotubes by the introduction of yne groups.
Similarly to ordinary nanotubes, arm-chair, zig-zag, and chiral graphyne
nanotubes are possible. Electronic properties, predicted using tight-binding
and ab initio density functional methods, show a rich variety of metallic and
semiconducting behaviors.
