[no subject]



  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).