Subject: Summary: ESP

From: [email-masked]
Date: Tue, 9 Jun 1998 10:14:17 +0900

Dear Sir:

        I would like to ask about determination of atomic charges from ab
initio electrostatic potentials:  For example, in CHELP, CHELPG, and Merz
and Kollman, various points were normally  putted at the van der Waals
contact region surrounding the molecule ?

        Thank you.

Masao Masamura
Preventive Dentistry
Okayama University Dental School
Shikata-cho, 2-5-1
Okayama 700
Japan
FAX: 81-86-235-6714
e-mail: [email-masked] 

Date: Tue, 26 May 1998 13:22:46 +0200
From: [email-masked] (Ulf Ryde)
To: [email-masked]
Subject: Re: CCL:ESP
X-UIDL: 76f2788761e07a72a5d44d1577ae3865

Dear Prof. Masamura,

we discuss related questions in our article:
E. Sigfridsson & U. Ryde (1998) A comparison of methods for deriving
atomic charges from the electrostatic potential and
moments. J. Comp. Chem. 19, 377-395. 

It is also described in an electronic poster:
http://garm.teokem.lu.se/~teoema/chargeposter.html

Best Regards,
Ulf
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Dr. Ulf Ryde                        [email-masked]
Assistant professor                 http://signe.teokem.lu.se/~ulf
Department of Theoretical Chemistry
University of Lund
Chemical centre, P. O. Box 124      Phone: +46-46-2224502
S-221 00, Lund, SWEDEN              Fax:   +46-46-2224543
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Dear Sir:

        In CHELMO and CHELP-BOW,  points can be putted within van der Waars
radii ?
 
        Thank you.

Date: Wed, 3 Jun 1998 07:24:23 +0200
From: [email-masked] (Ulf Ryde)
To: [email-masked]
Subject: Re:
X-UIDL: 0b23c747e0840b455770337f714df0d5

Dear Prof. Masamura,

in CHELMO, the charges are determined by a fit directly to the
electrostatic moments of the molecule. Therefore, no potential is used
and we do not have to decide what points to use.

In the CHELP-BOW method, the charges are determined by a fit to the
electrostatic potential as usual, but all points are Boltzmann-weighted
according to the distance between the potential point and the atoms in
the molecule using the potential function of the program in which the
charges will be used. Thus, points arbitrary close to any atoms in the
molecule are used (i.e. also within the van der Waals radius of the
atoms), but they will have a very small weight.

Best regards,
Ulf

Date: Sat, 30 May 1998 15:59:41 +0200
From: Konrad Hinsen <[email-masked]>
To: [email-masked]
Subject: Re: CCL:ESP
X-UIDL: b1a7d35d0fd869af7c95c5ffb21b6b64

>         I would like to ask about determination of atomic charges from ab
> initio electrostatic potentials:  For example, in CHELP, CHELPG, and Merz
> and Kollman, various points were normally  putted at the van der Waals
> contact region surrounding the molecule ?

Right, but the procedures differ in detail. And there are also other
methods. The two essential points in which charge fitting methods
differ are:

1) The choice of evaluation points. Grid-based points have many
   problems, mostly due to the dependence of the results on the
   grid axes. Points on shells or simple random points in a shell
   are better choices.

2) The fitting algorithm. CHELP and CHELPG use an algorithm that
   is known to be numerically unstable, leading to unrealistically
   high charges. The Merz/Kollman approach tries to get around this
   problem by adding charge constraints, but doesn't change the
   fit algorithm itself. An SVD-based least-squares fit is safer,
   and in fact this has been the standard least-squares algorithm
   for 20 years in all field except computational chemistry.

-- 
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Konrad Hinsen                          | E-Mail: [email-masked]
Laboratoire de Dynamique Moleculaire   | Tel.: +33-4.76.88.99.28
Institut de Biologie Structurale       | Fax:  +33-4.76.88.54.94
41, av. des Martyrs                    | Deutsch/Esperanto/English/
38027 Grenoble Cedex 1, France         | Nederlands/Francais
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