charges in CHARMm

["Don Gregory" <Don_Gregory \\at// msi.com>]

                        Subject:                               Time:8:22 AM
   OFFICE MEMO          charges in CHARMm                      Date:10/30/95
 On 30 Oct., Dr. Andrey Bliznyuk wrote asking about CHARMM(m) charges.
 Partial atomic charges have been developed in the CHARMm force-field
 in a consistent way, basically involving the ESP method published
 in the literature, followed by scaling so as to fit the intermolecular
 energies (obtained from ab initio calculations) between waters
 placed nearby the model compound. This procedure is detailed in the beginning
 of the CHARMm parameter handbook.
 In addition, a great deal of effort has been put into a facility
 named the "parameter chooser" within Quanta, which uses a rule-based
 approach to nominate charges as a first approximation.  These rules
 have been chosen to match, as closely as possible, those charges
 that have been developed in the above method, and allows then the
 user to extend to novel systems, by first deciding on atom-types
 in the local environment, then using the rules to suggest charges
 that the user can then change if so desired.
 Don Gregory
 Quanta/Protein Product Manager
 Biosym/Molecular Simulations