Subject: Re: CCL: CHELPG and MerzKollman

From: [email-masked] (正村)
Date: Wed, 8 Jan 1997 13:49:06 +0900

I have two answers for the following questions:

        I ask everybody about the selection of points for CHELPG and
MerzKollman in  Gaussian 94. 
How do the CHELPG and MerzKollman choose the point ? For example,  Point
which fall within the van der Waals radius of any of the atoms are
discarded ?  In CHELP, this is true.

        I thank everybody.  

Masao Masamura
Preventive Dentistry
Okayama University Dental School
Shikata-cho, 2-5-1
Okayama 700
Japan
FAX: 81-86-225-3724 
e-mail: [email-masked] 
         
<answer 1>

Date: Fri, 22 Nov 1996 11:51:32 -0600 (CST)
From: [email-masked]
Subject: Re: CCL:G:CHELPG and MerzKollman
To: [email-masked]
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CHelpG selects points based on a 3-dimensional rectangular
grid.  MerzKollman selects points on concentric van der Waals
shells of the molecule.  Both neglect any points within the 
vdw radius, as you mentioned.

In my experience, both methods give comparable results.

Kurt Grafton
University of Oklahoma
USA

<answer 2>

From: [email-masked] (Doug Fox)
Subject: Re: CCL:G:CHELPG and MerzKollman
To: [email-masked] (正村)
Date: Fri, 22 Nov 1996 13:08:53 -0500 (EST)
X-Mailer: ELM [version 2.4 PL24]
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    The charge fitting routines in G94 are faithful implementations of
the algorithms published by Chirlian/Francl (CHelp) , Brenneman and
Wiberg(ChelpG) and Merz and Kollman(MK).  Thus you can refer to the
original reference for details on the sampling algorithms.  The basic
details are,

    1) ChElP uses concentric spheres starting at the vanderWaals radii
       with interior points excluded.

    2) ChElPG uses a regular rectangular grid with points within the
       vanderWaals radii excluded.  There is also a distance criteria
       for the maximum distance from the atomic centers.

    3) MK uses nested solvent exclusion surfaces again excluding the
       volume within innermost surface which coincides in large part
       with the vanderWaals radii.

  The suggested vanderWaals radii for each element vary between the
authors and so the exclusion zone varies slightly between the methods.

  Douglas J. Fox
  Director of Technical Support
  [email-masked]