The C₆₀ Molecules in (C₆₀)_N@SWCNT Peapods: Crystal Field, Intermolecular Interactions and Dynamics

Abstract

We calculate the crystal field experienced by a single C₆₀ molecule encapsulated in a single‐walled carbon nanotube. We take the icosahedral symmetry of the C₆₀ molecule fully into account by treating it as a cluster of interaction centers. Although we do not distinguish between armchair, zig‐zag and chiral nanotubes since we consider a nanotube as a uniform cylindrical surface density, we can vary the tube radius R _T. We observe a flip of the lowest‐energy C₆₀ molecular orientation when increasing the radius: below R _T≈6.5 Å, the lowest energy occurs when two pentagons are perpendicular to the nanotube's long axis, while for higher values, an orientation with hexagons perpendicular to the tube's long axis is energetically more favorable. Then, we consider a linear chain of C₆₀ molecules inside a carbon nanotube, all experiencing the crystal field as a confinement potential. We find tube radius‐dependent effects: distinct equilibrium lattice spacings and lattice contractions. We calculate the structure factor and demonstrate the presence of pseudo‐Bragg peaks. Finally, we briefly comment on the calculation of infrared and Raman absorption spectra within the presented framework.

Keywords:

• Carbon peapod
• fullerene C₆₀
• intermolecular interactions
• theoretical calculations
• IR spectrum

Acknowledgments

We thank P. Launois and D. Lamoen for useful discussions. The present work has been supported by the Bijzonder Onderzoeksfonds, Universiteit Antwerpen (BOF–NOI). B.V. is a research assistant of the Fonds voor Wetenschappelijk Onderzoek‐Vlaanderen.