Christof Hättig^a,c, Georg Jansen^b,d, Bernd Artur Heß^a, and Janós G. Ángyán^b,
^aInstitut für Physikalische und Theoretische Chemie, Universität Bonn, Wegelerstr. 12, D-53115 Bonn, Germany
^bLaboratoire de Chemie Théorique, Université de Nancy I, URA CNRS No. 510, B.P. 239, F-54506 Vandoeuvre-lès-Nancy Cedex, France
^cPresent address: Department of Chemistry, Århus University, DK-8000 Århus C, Denmark
^dPresent address: Institut für Theoretische Chemie, Universität Düsseldorf, Universitätsstraße 1, D-40225 Düsseldorf, Germany

Mol. Phys. 91, 145-160 (1997) (Received 16 September 1996; accepted 6 January 1997)

Multicentre multipole expansions allow to solve the `shape' convergence problem arising in the calculation of long-range interaction energies between large non-spherical molecules via point-multipole expansions. In paper I of this series (1996, Molec. Phys., 88 69) it has been shown that this is the case for first-order electrostatic and second-order induction energies when employing distributed multipole moments and static polarizabilities generated from topological partitioning of the molecular volume as provided by Bader's `atoms-in-molecules' theory. Their generalization to frequency-dependent, topologically partitioned polarizabilities is used in the present contribution to compare the convergence behaviour of one-centre and multicentre multipole expansions of the second-order dispersion energy for homonuclear dimers of the water, carbon monoxide, cyanogen and urea molecules. The findings are similar to those for the induction energy: the radial `extension' convergence problem, which exists already for point-multipole expanded interaction energies between atoms, necessarily persists, but the angular convergence problems linked to the shape of interacting molecules can succesfully be treated by multicentre multipole expansions of the dispersion energy.

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