Physical Review B
(Condensed Matter and Materials Physics -15(II))

Phys. Rev. B, 70, 205418 (2004)
URL: http://link.aps.org/abstract/PRB/v70/e205418
doi:10.1103/PhysRevB.70.205418
PACS: 61.46.+w

Energetics and structural characterization of C₆₀ polymerization in BN and carbon nanopeapods

Andrea Trave, Filipe J. Ribeiro, Steven G. Louie, and Marvin L. Cohen

Department of Physics, University of California, Berkeley, California 94720, USA and Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA

As in the case of carbon nanotubes, also boron nitride nanotubes may host arrays of C₆₀ molecules and form a nanopeapod (NPP). The observed separation between C₆₀ molecules in BN NPP's is consistently shorter than in carbon NPP's, which influences their electronic properties. Here we report on total-energy pseudopotential density functional theory (DFT) calculations for polymerized and nonpolymerized C₆₀ chains, and optimize their atomic structures to provide a description of their energetic landscape. A fully polymerized C₆₀ chain and a C₆₀ dimer are found to be more stable than nonpolymerized C₆₀, respectively, by 0.89 and 0.38 eV/C₆₀. The geometry and energetics of an encapsulated C₆₀ chain is not significantly different with respect to the isolated molecule. Encapsulation energies in BN and carbon NPP's are, respectively, 1.56 and 1.67 eV/C₆₀, which are significantly large than the calculated activation energy for C₆₀ polymerization, supporting the hypothesis that encapsulated C₆₀'s in NPP's are partially polymerized. Band structure analysis show that polymerization does not affect the gap width of the C₆₀ chain. BN NPP's are semiconductors with a gap width determined by the C₆₀. The lowest unoccupied C₆₀ states lie just above the Fermi level in metallic carbon NPP's and charge transfert could take place, affecting the C₆₀ geometry.