[ 2011.10.10 ] Dynamics of benzene molecules situated in metal-organic frameworks (Yue Chan and James M. Hill)

We investigate the gyroscopic motion of a benzene molecule inside a metal-organic framework which provides a sterically unhindered environment and an electronic barrier for the benzene molecule. We model the inter-molecular interactions between the benzene ring and the metal-organic framework by both the Columbic and van der Waals forces. We also capture additional molecular interactions, for example due to sterical compensations arising from the carboxylate ligands between the benzene molecule and the framework, by incorporating an extra empirical energy into the total molecular energy. We firstly investigate the freely suspended benzene molecule inside the framework, and find that our theoretical results admit a two-fold flipping with the possible maximum rotational frequency reaching the terahertz regime and gigahertz frequencies at room temperature. The electrostatic interaction and the thermal energy turn out to dominate the gyroscopic motion of the benzene molecule. We also deduce that the extra energy term could possibly reduce the rotational frequency of the rigidly suspended benzene molecule from gigahertz to megahertz frequencies, and even lower frequencies might be reached when the strength of the extra energy increases. (Picture: (Copyright-American Chemical Society 2008).)

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[ 2011.08.05 ] Modelling the surface adsorption of methane on carbon nanostructures (Olumide O. Adisa, Barry J. Cox and James M. Hill)

Methane (CH₄) adsorption is investigated on both graphite and in the region between two aligned single-walled carbon nanotubes, which we refer to as the groove site. We exploit the Lennard–Jones potential function and the continuous approximation to determine surface binding energies between a single CH₄ molecule and graphite and between a single CH₄ and two aligned single-walled carbon nanotubes. Our results confirm the current view that for larger groove sites, CH₄ molecules in grooves are likely to move towards the outer surfaces of one of the single-walled carbon nanotubes. Our results are computationally efficient and are in good agreement with experiments and molecular dynamics simulations, and show that CH₄ adsorption on graphite and groove surfaces is more favorable at lower temperatures and higher pressures .

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[ 2011.07.28 ] A two-state shuttle memory device (Richard K. F. Lee and James M. Hill)

A nanomemory device comprises a metallofullerene inside a closed carbon nanotube. The mechanics of a metallofullerene shuttle memory device is investigated by the 6-12 Lennard-Jones potential using the continuum approximation, which assumes that a discrete atomic structure can be replaced by an average atomic surface density. It shows the system has two equal minimum energy positions, which are symmetrically located close to the tube extremities, and therefore it gives rise to the possibility of being used as a two-state memory device. On one side the encapsulated metallofullerene represents the zero information state and by applying an external electrical field, the metallofullerene can overcome the energy barrier of the nanotube, and pass from one end of the tube to the other end, where the metallofullerene then represents the one information state.

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