B. Verberck

Nanotube field of C60 molecules in carbon nanotubes: atomistic versus continuous tube approach

We calculate the van der Waals energy of a

Superposition of quantum and classical rotational motions in Sc2C2@C84 fullerite

{\mathrm{C}}_{60}

Crystal structures of polymerized fullerides AC60, A=K, Rb, Cs, and alkali-mediated interactions

molecule when it is encapsulated in a single-walled carbon nanotube with discrete atomistic structure. Orientational degrees of freedom and longitudinal displacements of the molecule are taken into account, and several achiral and chiral carbon nanotubes are considered. A comparison with earlier work where the tube was approximated by a continuous cylindrical distribution of carbon atoms is made. We find that such an approximation is valid for high and intermediate tube radii; for low tube radii, minor chirality effects come into play. Three molecular orientational regimes are found when varying the nanotube radius.

Orientational ordering in solid C60 fullerene-cubane

The superposition of the quantum rotational motion (tunneling) of the encapsulated Sc(2)C(2) complex with the classical rotational motion of the surrounding C(84) molecule in a powder crystal of Sc(2)C(2)@C(84) fullerite is investigated by theory. Since the quantum rotor is dragged along by the C(84) molecule, any detection method which couples to the quantum rotor (in casu the C(2) bond of the Sc(2)C(2) complex) also probes the thermally excited classical motion (uniaxial rotational diffusion and stochastic meroaxial jumps) of the surrounding fullerene. The dynamic rotation-rotation response functions in frequency space are obtained as convolutions of quantum and classical dynamic correlation functions. The corresponding Raman scattering laws are derived, and the overall shape of the spectra and the width of the resonance lines are studied as functions of temperature. The results of the theory are confronted with experimental low-frequency Raman spectra on powder crystals of Sc(2)C(2)@C(84) [M. Krause et al., Phys. Rev. Lett. 93, 137403 (2004)]. The agreement of theory with experiment is very satisfactory in a broad temperature range.

The C60 molecules in (C60)N@SWCNT peapods: crystal field, intermolecular interactions and dynamics

Starting from a model of rigid interacting C60 polymer chains on an orthorhombic lattice, we study the mutual orientation of the chains and the stability of the crystalline structures Pmnn and I2/m. We take into account (i) van der Waals interactions and electric quadrupole interactions between C60 monomers on different chains as well as (ii) interactions of the monomers with the surrounding alkali atoms. The direct interactions (i) always lead to an antiferrorotational structure Pmnn with alternate orientation of the C60 chains in planes (001). The interactions (ii) with the alkalis consist of two parts: translation-rotation (TR) coupling where the orientations of the chains interact with displacements of the alkalis, and quadrupolar electronic polarizability (ep) coupling, where the electric quadrupoles on the C60 monomers interact with induced quadrupoles due to excited electronic d-states of the alkalis. Both interactions (ii) lead to an effective orientation-orientation interaction between the C60 ch...

Ordered and disordered packing of coronene molecules in carbon nanotubes

We study the structure and phase behavior of fullerene-cubane C(60) x C(8)H(8) by Monte Carlo simulation. Using a simple potential model capturing the icosahedral and cubic symmetries of its molecular constituents, we reproduce the experimentally observed phase transition from a cubic to an orthorhombic crystal lattice and the accompanying rotational freezing of the C(60) molecules. We elaborate a scheme to identify the low-temperature orientations of individual molecules and to detect a pattern of orientational ordering similar to the arrangement of C(60) molecules in solid C(60). Our configuration of orientations supports a doubled periodicity along one of the crystal axes.

Fullerene-cubane: X-ray scattering experiments and Monte Carlo simulations

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 nanotubes long axis, while for higher values, an orientation with hexagons perpendicular to the tubes 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.

Valence electronic charge density of distorted C60− monomers in polymerized KC60 and RbC60

Monte Carlo simulations of coronene molecules in single-walled carbon nanotubes (SWCNTs) and dicoronylene molecules in SWCNTs are performed. Depending on the diameter D of the encapsulating SWCNT, regimes favoring the formation of ordered, one-dimensional (1D) stacks of tilted molecules (D ≤ 1.7 nm for coronene@SWCNT, 1.5 nm ≤ D ≤ 1.7 nm for dicoronylene@SWCNT) and regimes with disordered molecular arrangements and increased translational mobilities enabling the thermally induced polymerization of neighboring molecules resulting in the formation of graphene nanoribbons (GNRs) are observed. The results show that the diameter of the encapsulating nanotube is a crucial parameter for the controlled synthesis of either highly ordered 1D structures or GNR precursors.

A portrait of cadmium

We report single‐crystal X‐ray diffuse scattering measurements on C60.C8H8 fullerene‐cubane showing that the C60 molecules are orientationally disordered at 300 and 150 K and get ordered at low temperatures. Monte Carlo simulations provide further insight in the orientational behavior of both C60 and C8H8 molecules; low‐temperature molecular orientations are predicted.

Monte Carlo Studies of C60- and C70-Peapods

We investigate the valence electronic charge density of the C(60) (-) monomers in (C(60) (-))(n) polymer chains in K- and RbC(60) by means of a nonorthogonal tight-binding formalism using experimental data on the positions of the carbon atoms. Various configurations of the C(60) cages are considered. Starting from the ideal icosahedral C(60) structure and moving to the realistic, experimentally determined spatial configuration of the C(60) cages in K- and RbC(60), we observe a systematic increase of the electric quadrupole moments on the C(60) (-) monomers. We also confirm the validity of factorizing the charge density of a C(60) (-) monomer into an angular and a radial part.