Computations of model narrow nanotubes closed by fragments of smaller fullerenes and quasi-fullerenes
New type of carbon nanotubesnarrow nanotubeshas recently been observed with diameters of 45. It has been postulated that the narrow nanotubes are closed by fullerene fragments of C20 and C36. This paper presents computational results on related model nanotubes with stoichiometries such as C80, C84, C96, C108, or C120. The computations were carried out at the PM3, AM1, SAM1, HF/3-21G, HF/4-31G, and B3LYP/6-31G? levels. Two C36 fullerenes were considered, D6h and D2d. At the PM3 level and with the C84 nanotube stoichiometry, the D2d cage closure gave a lower energy (by 185kcal/mol and a diameter of 5.42). There is another possible candidate, a C32 cage with D4d symmetry (two four-membered rings). At the PM3 level and with the C96 nanotube stoichiometry, the D4d closure (with a diameter of 5.43) had energy lower by 210kcal/mol than that of the D6h nanotube closure. On the other hand, four-membered rings should not play a significant role for narrow nanotubes with a diameter of 4, where the dodecahedron-related closure should be exclusive. Still narrower nanotubes are briefly discussed.
narrow nanotubes smaller fullerenes c20 c36 four-membered rings