Room temperature Peierls distortion in small radius nanotubes
  By means of {\it ab initio} simulations, we investigate the phonon band structure and electron-phonon coupling in small 4-\AA diameter nanotubes. We show that both the C(5,0) and C(3,3) tubes undergo above room temperature a Peierls transition mediated by an acoustical long-wavelength and an optical $q=2k_F$ phonons respectively. In the armchair geometry, we verify that the electron-phonon coupling parameter $\lambda$ originates mainly from phonons at $q=2k_F$ and is strongly enhanced when the diameter decreases. These results question the origin of superconductivity in small diameter nanotubes. 
D. Connetable (LPMCN), G.-M. Rignanese (PCPM, Cermin), J.-C. Charlier   (PCPM, Cermin), Xavier Blase (LPMCN)