Potential energy surfaces of several van der Waals complexes modelled using distributed multipoles

We report analyses of the potential energy surfaces of five van der Waals complexes, Ar-NH3, ((CH3)2NH)2, propene-SO2, acetylene-N2 and acetylene-CO described by a potential based upon distributed multipoles for the electrostatics and atom-atom Lennard-Jones terms for the dispersion-repulsion. In particular we describe the low energy rearrangement mechanisms in each system, and compare these results with those of previous studies, especially experimentally observed tunnelling splittings. Our results are mixed, probably due to the description of the dispersion-repulsion terms, although even in the worst cases the structures we find will serve as useful starting points for ab initio work. Improvement of the dispersion and repulsion terms in acetylene-N2 and acetylene-CO gives much better results.