Intermolecular perturbation theory for Van der Waals molecules
We report an application to some Van der Waals systems of a perturbation analysis of the energy of interaction between the component molecules. The method used differs from the procedure reported previously, in that an expansion in powers of overlap is not required and errors from basis set superposition are corrected. The total interaction energy is obtained as a sum of terms, which can be identified as electrostatic, exchange, repulsion, charge transfer, etc. The individual terms are now less dependent on basis set than before (except that an improvement in basis set is reflected in a larger polarisation energy) and the total energies agree satisfactorily with supermolecule calculations in which the counterpoise method is used to correct for superposition error.