Lennard-Jones interaction for hexagonal layered crystals

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Abstract
A very wide range of extremely high precision single‐plane hexagonal lattice sums were calculated by computer. These sums are necessary to the Lennard‐Jones interaction potential theory for hexagonal layered crystals. As an application, interplanar spacing, c‐axis lattice energy, c‐axis elastic moduli, and their change with compressive strain were obtained for all known graphites having ordered stacking. Theoretical results consistently compared well with available experiment, except for cases involving c‐axis shear or in‐plane translation, where serious underestimation was the rule. Substantial errors in an earlier major calculation for ABA graphite, also using precise lattice sums, became apparent. While it was concluded here that the Lennard‐Jones interaction potential is satisfactory otherwise, it fails completely to describe correctly changes in graphite related to atomic movements in the c plane. This limited success may, indeed, be merely incidental rather than fundamental.