  We present a comparative study of the energetic, structural and elastic
properties of carbon and composite single-wall nanotubes, including BN, BC3 and
BC2N nanotubes, using a non-orthogonal tight-binding formalism. Our
calculations predict that carbon nanotubes have a higher Young modulus than any
of the studied composite nanotubes, and of the same order as that found for
defect-free graphene sheets. We obtain good agreement with the available
experimental results.
