Novel polygonized single-wall carbon nanotube bundles

We have synthesized novel crystalline ropes of "polygonized" single-wall ca rbon nanotubes (SWCNTs). The tubes exhibit rounded-hexagonal cross sections in contrast to the earlier observations of nearly circular tubes. To inves tigate the structural characteristics of the lattice of SWCNTs we have perf ormed extensive molecular-dynamics simulations. We find several metastable structures of the lattice characterized by different tube cross sections, h exagonal, rounded-hexagonal, and circular, and increasing cell volume. The competition between different tube shapes as a function of tube diameter is analyzed and compared to experiments.