INTERMOLECULAR INTERACTION ENERGIES BY TOPOLOGICALLY PARTITIONED ELECTRIC PROPERTIES .1. ELECTROSTATIC AND INDUCTION ENERGIES IN ONE-CENTERAND MULTICENTER MULTIPOLE EXPANSIONS

Certain difficulties with the usual one-centre multipole expansion of long-range intermolecular interaction energies can be circumvented by multicentre multipole expansions using several expansion sites in each molecule, such as, e.g., the nuclear positions. Based on the topologi cal partitioning of the molecular volume provided by Bader's 'atoms in molecules' theory, a method has been developed for calculating the re quired atomic multipole moments and polarizabilities. The performance of these topologically partitioned electric properties is examined for the calculation of multipole expanded first-order electrostatic and s econd-order induction energies by comparing their convergence behaviou r with that of the corresponding one-centre expansions. The homomolecu lar dimers of the water, carbon monoxide, cyanogen, and urea molecules serve as examples. The results show that distributed electric propert ies calculated within the topological partitioning scheme indeed solve the 'shape' convergence problem, which arises in the calculation of i nteraction energies of large non-spherical molecules via multipole exp ansions.