Abstract Submitted to the ; NANOTUBE'05 Conference:

First-principles calculations are performed to investigate the electronic, structural, and vibrational properties of single-wall carbon nanotubes with very small diameters. In particular, we focus on the (3,3), (4,2), and (5,0) tubes which are potential candidates for the 4 Å-diameter tubes synthesized inside zeolite channels. With such a narrow diameter,the electronic properties of these nanotubes near the Fermi level cannot be understood starting from the graphene sheet model, although this zone folding model is quite successful in the case of large diameter tubes. Our results indicate that perfectly-cylindrical (3,3) and (5,0) tubes are metallic, while the (4,2) tube is semiconducting with a small indirect band gap. The calculated radial breathing modes agree with experimentally measured Raman spectrum, giving strong support that these small radius tubes are indeed present inside zeolite crystals.
However, the dynamical properties of the both the (5,0) and (3,3) nanotubes suggest the structures to be metastable in its cylindrical form. Above room temperature, both the C(5,0) and C(3,3) tubes are found to undergo a Peierls transition which is mediated by an acoustical long-wavelength and an optical q=2kF phonons respectively. In the armchair geometry, the electron-phonon coupling parameter ? originates mainly from phonons at q=2kF and is strongly enhanced when the diameter decreases. These results question the origin of superconductivity in small diameter nanotubes.
References:
[1]. D. Connétable, G.M. Rignanese, J.-C. Charlier and X. Blase, Physical Review Letters 94, 015503 (2004).

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