A new approach to empirical intermolecular and conformational potential energy functions. I. Description of model and derivation of parameters.

An empirical potential energy function based on the interactions of the electrons and nuclei in molecules has been developed and tested. The potential energy of interaction is approximated by the sum of the coulombic interactions between all point charge centers (electrons and nuclei), an exponential repulsion to represent electron-electron overlap repulsion, and an R(-6) (R = distance) attraction to simulate dispersion and other attractive energies between the heavy atom fragments of the molecules. The parameters of the potential energy function have been determined from experimental gas-phase and crystal data.The results indicate that both intramolecular and intermolecular interaction energies can be treated with the same set of parameters. In comparison to other empirical interaction potentials now in use, there are fewer independent parameters, there is no need for intrinsic torsional potentials to obtain the correct rotational barriers, and there is no need for special hydrogen bonding functions to account for the directionality and energetics of hydrogen bonding.