Subject: Re: CCL:ESP charges

From: Julian Tirado-Rives <Julian.Tirado-Rives~at~yale.edu>
Date: Wed, 5 Nov 2003 09:13:58 -0500 (EST)

Dear Daniela:

    Actually, there is no problem ...  most of the OPLS charges are not really
ESP, although for many cases that is our typical "starting guess". We usually
arrive to the final non-bonded parameters for a given type of molecule
in an iterative fashion in which we try to reproduce through actual simulations
as many experimentally (well-) determined thermodynamic parameters as we can
find for one or more molecules of the same type, typically pure liquid
densities, heats of vaporization, free energies of solvation, rdf's if
available, etc.  In the course of the iterations we may (but not always do)
vary both the Lennard-Jones parameters and the charges while trying to balance
the precision of the results with the generality, number of atomic types in
the FF, etc.

   I hope this answer your question, but if you have further doubts feel free
to email me.

   Good Luck!

                                          - Julian -

Daniela Dogaru <d.dogaru~at~csuohio.edu> wrote:
> Dear all,
> I have a question regarding the ESP charges which are used in OPLS 
> parameters from MD programs like Gromacs .  I got some discrepancies 
> between the OPLS charges I calculate with Gaussian and the ones that 
> are implemented in Gromacs force field , for Tyrosine residue.
> What do you think will be the problem?
> My best wishes!
> Daniela
> 

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   |  Julian Tirado-Rives          |                                      |
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