Ab initio-based intermolecular carbon-carbon pair potentials for polycyclic aromatic hydrocarbon clusters.

We derived the carbon-carbon pair potentials for polycyclic aromatic hydrocarbon (PAH) clusters, which exhibited a strikingly similar geometry to that of the two-layer graphite. The binding energy of PAH clusters ranging in size from the benzene dimer to the pyrene dimer obtained by ab initio calculations at the MP2 level was used to extract the pair potentials in the form of the Lennard-Jones and Exponential-6 functions. Identical binding energy and equilibrium interlayer distance were reproduced by these functions to those calculated by the ab initio method. The pair potentials for PAHs yield the same equilibrium C-C distance as the known pair potentials for graphite and fullerenes, but nearly twice the well depth because of the polarization of the C-H bond.