Lennard-Jones-potential Calculation of C60 Stage-One Graphite.

The potential energies per atom of pure graphite and of ${\mathrm{C}}_{60}$ stage-one graphite intercalation compound (GIC) are compared in a calculation based on summing pairwise a Lennard-Jones 12-6 potential between all mass points with parameters taken from previous calculations on pure graphite. The C atoms are treated as uniformly smeared onto rigid spheres and rigid planes. For graphite the potential has a minimum of -46 meV/atom at an interplanar spacing of 3.37 \AA{} with a compressibility of 3.0\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}12}$ ${\mathrm{cm}}^{2}$/dyn. For the GIC, assuming a triangular ${\mathrm{C}}_{60}$ net, the minimum is -22 meV/atom occurring at both a ${\mathrm{C}}_{60}$-graphene and a ${\mathrm{C}}_{60}$-${\mathrm{C}}_{60}$ nearest approach distance of 2.9 \AA{}. This distance is comparable to fcc ${\mathrm{C}}_{60}$ at room temperature. The calculated compressibility is 3.8\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}12}$ ${\mathrm{cm}}^{2}$/dyn.