An intermolecular potential function model applied to acetylene dimer, carbon dioxide dimer, and carbon dioxide acetylene

A general model to describe intermolecular potential functions for weakly bound molecular complexes is described. The model is designed to be complex enough to reproduce many observed details of van der Waals molecules, yet be simple enough that the required input data are readily available. The distributed multipole picture of monomer charge distributions is used to calculate electrostatic energies and atom–atom Lennard-Jones terms describe repulsion and dispersion. The individual atom C6 coefficients are derived from long-range molecular C6 values and the C12 coefficients are based on conventional van der Waals atomic radii. This model is applied to (HCCH)2, (CO2)2, and HCCH–CO2. The resulting potential functions are compared in detail, with particular emphasis placed on understanding why (HCCH)2 and (CO2)2 have such different structures.