Mechanical interactions in all-carbon peapods

Structures and energetics of several types of all-carbon peapods made by C(60)s encapsulated inside single-wall carbon nanotubes are calculated. The interactions between the tubes and the molecules determine a minimal diameter for exothermic encapsulation of 11.74 Angstrom and a radial deformation of the C-60 cage that is a linear function of the tube diameter. Many relative orientations of the "peas" have similar energies and can be thermally equilibrated, although preferential ways of interaction between fullerenes do exist. In particular, for a triplet of embedded fullerenes, the lowest energy arrangement is characterized by a facing describable as pentagon-hexagon-pentagon. The activation energy for the translation of isolated C-60 molecules inside the tubes is very low and an isolated C-60 can diffuse freely inside the pod: The major factor controlling the dynamics of molecular transport in the peapods is therefore the C-60-C-60 interaction.