Nanotube field of C-60 and C-70 molecules in carbon nanotubes

摘要

We calculate the van der Waals energy of a C-60 or a C-70 fullerene molecule encapsulated in a single-walled carbon nanotube (SWCNT). Orientational. degrees of freedom and longitudinal displacements of the molecule are taken into account; calculations are performed for a representative selection of achiral and chiral carbon nanotubes. A simplifying approach, approximating the tube as a continuous cylindrical distribution of carbon atoms, thus focusing on the radius dependence only rather than on the full chirality dependence, is presented. For both fullerene molecules the specific molecular symmetry and the tube symmetry are maximally exploited by using symmetry-adapted rotator functions. For C-70, three molecular orientational regimes can be distinguished upon varying the nanotube radius; the smooth-tube approximation is valid for high and intermediate tube radii (>= 7 angstrom) while for low radii (<= 7 angstrom) minor chirality effects come into play. For C-70, the continuous-tube approximation works extremely well; we find that for low (<= 7 angstrom) tube radii the "lying" molecular orientation is favorable while for high (>= 7.2 angstrom) radii, the "standing" orientation is recovered-well in agreement with recent X-ray diffraction experiments. The possibility of having transversally displaced molecules is investigated. Chains of C-60 and C-70 molecules are studied; a one-dimensional liquid description of linear chains of C-60 or C-70 molecules inside a SWCNT is set up. (c) 2007 Wiley Periodicals, Inc.