Dear Francois,
 I'm not familiar with the specific CHELPG modifications made for GAMESS, but one
 issue with the original CHELPG routine was the possibility of computing atomic
 charges that do not coincide with molecular symmetry.  In the original
 implementation, no special attention was paid to assuring that the 3D  grid of
 sampled points was symmetrically distributed with respect to molecular symmetry
 elements.  The effect can result in unequal ESP charges being computed for
 symmetrically-related atoms.   This is not always a problem - In fact, it was
 that for small molecules using dense grids, (0.2 au or so), this was a minor
 In practical applications, this can raise an issue. The variation can be large
 small, depending upon the complexity of the electrostatic field and the sparsity
 the sampling grid.
 Curt Breneman
 RPI Chemistry
 FyD wrote:
 > Dear All,
 > I am trying to use CHELPG in GAMESS to get electrostatic potential. In the
 > GAMESS doc., it is written:
 > "CHELPG: to use a modified version of the CHELPG algorithm, which
 produces a
 > symmetric grid of points for a symmetric molecule"
 > - Does it mean that the CHELPG algorithm in GAMESS is different from the
 > published one in Breneman & Wiberg, J Comput Chem 1990, 11, 361-373 ?
 > - If yes, why this algo. has been modified in GAMESS and/or is there a way
 to use
 > the original one in GAMESS ?
 > Thanks, regards, Francois
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