From chemistry-request;at;ccl.net Fri Feb 14 11:04:34 1992 Date: Fri, 14 Feb 92 09:53:26 EST From: Kurt.Hillig: at :um.cc.umich.edu To: chemistry -A_T- ccl.net Status: R As a side note to the question of calculating atomic charges, there has been a lot of discussion in the literature of methods for structural prediction for van der Waals dimers. It's generally accepted that electrostatic interactions are a major contributor to the overall interaction. In general, methods based on atomic charges alone do not predict the structures or binding energies well. Furthermore, methods based on the distributed multipole model of Buckingham, Fowler and Stone appear to work fairly well only when one of the partners of the dimer is non-polar (e.g. in C2H4 - SO2), but usually fails when both components are polar (as in (SO2)2). What does it all mean? My best interpretation is that you need to be very careful when applying simple electrostatic models to intermolecular interactions. (Profound, isn't it?) So, I emphasize the cautions given about charge calculations - reliability is hard to define and harder to quantify (and, unfortunately, often impossible to achieve).