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The lattice summations of the potential energy of importance in the graphite system have been computed by direct summation assuming a Lennard-Jones 6–12 potential between carbon atoms. From these summations, potential energy curves were constructed for interactions between a carbon atom and a graphite monolayer, between a carbon atom and a graphite surface, between a graphite monolayer and a semi-infinite graphite crystal and between two graphite semi-infinite crystals. Using these curves, the equilibrium distance between two isolated physically interacting carbon atoms was found to be 2.70 a, where a is the carbon-carbon distance in a graphite sheet. The distance between a surface plane and the rest of the crystal was found to be 1.7% greater than the interlayer spacing. Theoretical values of the energy of cohesion and the compressibility were calculated from the potential curve for the interaction between two semi-infinite crystals. They were ΔEc = —330 ergs/cm2 and β = 3.18×10—12 cm2/dyne, respectively. These compared favorably with the experimental values of ΔEc = —260 ergs/cm2 and β = 2.97×10—2 cm2/dyne.
Girifalco et al. (Mon,) studied this question.