Molecular properties for two aggregates of C-60 and a (16, 0) zigzag nanotube: (a) C-60 encapsulated in the nanotube, (b) C-60 attached to the outer wall of the nanotube, are studied using the self-consistent charge density-functional tight-binding method with additional dispersion correction. The binding energy for the encapsulated fullerene is -108.3 kcal/mol and for the attached fullerene, only -20.3 kcal/mol. The harmonic vibrational frequencies of the aggregates are found to be almost identical to those obtained for the non-interacting system. Very small extent of the changes upon interaction may pose a challenge to study the aggregated structures using experimental spectroscopic methods. (C) 2007 Elsevier B.V. All rights reserved.