Abstract
Four hydrocarbon van der Waals potentials have been employed to obtain crystal unit cell dimensions and enthalpy sublimation values for two fullerenes, C 60 and C 70. The same force fields have also been employed in computing adsorption energies between a series of hydrocarbon molecules and a model graphite basal plane. The four hydrocarbon force fields are MM2, MM3, MM3hc, which is a new reparametrization of MM3 by the authors in earlier studies, and the potential of Williams and Starr. The MM3 and MM3hc force fields have been shown to offer the best agreement between the experimental and calculated crystal data for C 60 and C 70. In the graphite-adsorbate molecule computations, both charged and uncharged models for the four force fields have been tested to establish which model provides the most accurate structural and thermodynamic results. These calculations indicate that models with no charges are superior despite their deficiencies. For the adsorption of aliphatic molecules onto graphite, MM3hc yields closer agreement between experimental and calculated energies of adsorption than its counterparts, while its predictions for aromatic compounds are slightly less accurate than the MM2 and MM3 results. All force fields are similar in their predictions of structural arrangements of the adsorbate molecules on graphite. However, the computed structures disagree with experimental findings in several cases, underlining the inadequacy of simple analytical potential functions for graphite-hydrocarbon interactions.
Published Version
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