title: Computations of model narrow nanotubes closed by fragments of smaller fullerenes and quasi-fullerenes.
abstract: New type of carbon nanotubes-narrow nanotubes-has recently been observed with diameters of 4-5 A. It has been postulated that the narrow nanotubes are closed by fullerene fragments of C(20) and C(36). This paper presents computational results on related model nanotubes with stoichiometries such as C(80), C(84), C(96), C(108), or C(120). The computations were carried out at the PM3, AM1, SAM1, HF/3-21G, HF/4-31G, and B3LYP/6-31G(*) levels. Two C(36) fullerenes were considered, D(6h) and D(2d). At the PM3 level and with the C(84) nanotube stoichiometry, the D(2d) cage closure gave a lower energy (by 185 kcal/mol and a diameter of 5.42 A). There is another possible candidate, a C(32) cage with D(4d) symmetry (two four-membered rings). At the PM3 level and with the C(96) nanotube stoichiometry, the D(4d) closure (with a diameter of 5.43 A) had energy lower by 210 kcal/mol than that of the D(6h) nanotube closure. On the other hand, four-membered rings should not play a significant role for narrow nanotubes with a diameter of 4 A, where the dodecahedron-related closure should be exclusive. Still narrower nanotubes are briefly discussed.
authors.affiliation: Institute of Chemistry, Academia Sinica, 128 Yen-Chiu-Yuan Road, Sec 2, Nankang, Taipei 11529, Taiwan ROC. zdenek@ims.ac.jp
authors.forename: Zdenek
authors.initials: Z
authors.lastname: Slanina
authors.forename: Filip
authors.initials: F
authors.lastname: Uhlík
authors.forename: Ludwik
authors.initials: L
authors.lastname: Adamowicz
mesh_terms: D037741:Fullerenes / Q000737:chemistry*; D008958:Models, Molecular; D037742:Nanotubes, Carbon / Q000737:chemistry*
chemical_list: D037741:Fullerenes; D037742:Nanotubes, Carbon