Mulliken charges are asigned by apportioning the electrons in the overlap
 region between two atoms (two center overlap integrals) equally between the
 atoms, which are then added to the net atomic populations (from the
 one-center overlap integrals). Like most such schemes, it is an arbitrary
 scheme for assigning charges (since "atomic charges" are not
 defined, at least outside of Bader's AIM theory).
 If one wants to reproduce the electrostatic effects of the electron charge
 distribution in a molecule with reasonable accuracy, without arbitrary
 parametrization, one can employ either:
 * a distribution of point charges (i.e. monopoles) fitted to the
 electrostatic potential -- this is exactly what the CHELPG procedure does;
 * a distribution of monopoles, dipoles, quadrupoles and higher-order
 multipoles -- we have implemented this in a version of our RECON algorithm:
 Whitehead, Sukumar and Breneman, submitted to J. Comp. Chem.
 The original reference for CHELPG (CHarges from ELectrostatic Potentials
 Grid) is:
 "Determining Atom-Centered Monopoles from Molecular Electrostatic
 Potentials.  The Need for High Sampling Density in Formamide Conformational
 J. Comput. Chem., 11, 361-373 (1990) Curt M. Breneman and Kenneth B. Wiberg
 Dr. N. Sukumar
 Rensselaer Department of Chemistry
 On Tue, 09 Jul 2002 14:20:56 +0000 "George Hall" wrote:
 > Hi everybody,
 > I wonder if some could point me out what are the differences between
 > Chelpg
 > charges and Mulliken.
 > Would you please indicate me some references or some advices about the
 > aproach for these kind of charges.
 > Thanks a lot in advance.
 > George Hall.
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