Do Carbon Nanotubes Spin When Bundled?

Using ab initio and parametrized techniques, we determine the equilibrium structure of an ordered “bundle” of (10,10) carbon nanotubes. Because of small intertube interaction and lattice frustration, we predict a very soft libration mode to occur at v ≈ 12 cm−1. This mode is predicted to disappear above the orientational melting temperature which marks the onset of free tube rotations about their axis. We discuss the effect of the weak intertube coupling and orientational disorder on the electronic structure near the Fermi level.