Subject: Re: CCL:Dielectric in Charmm

From: Don Gregory <[email-masked]>
Date: Thu, 27 Jul 2000 08:26:11 -0700

Hi Michael, and Xiang,
I would only slightly disagree with Michael's statement that
"it is questionable to set these parameters to a value other than one"
in that what one should generally use, are those parameters that
were used to optimize the force-field originally.
If certain partial chargers, and/or vdw terms were adjusted with
an E14FAC set to 0.5, and then you use it at 1.0, one runs the
risk of over evaluating those terms.
In CHARMm, one can see the 'recommended' parameter
values by looking at the 'NBONDED' command section in the text
version of the parameter file.
Hope this helps!
Don Gregory

At 11:45 AM 7/27/00 +0100, Michael Brunsteiner wrote:
>"Xiang(Simon) Wang" wrote:
> >
> > Dear CCLers,
> >
> > When setting up the dielectric constant in charmm, what's the difference
> > between [ EPS real ] and [ E14Factor real ]?
>
>i believe that E14Factor only applies to 1-4 interactions,
>i.e. interactions between atoms in the same molecule separated by
>three bonds ... however, it is questionable to set these parameters
>to a value other than one anyway ...
>i'd always let EPS = E14Factor = 1.0 and use Ewald summation.
>
>mic
>
>
>
>===========================================================
>Writing software is more fun than working.
>
>----------------------------------------
>Michael Brunsteiner
>Centre for Theoretical and Computational Chemistry
>University College London
>20 Gordon Street, London WC1H 0AJ,  U.K.
>mailto:[email-masked]
>http://www.unet.univie.ac.at/~a8805193
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Dr. Don Gregory ([email-masked])
CHARMm Product Marketing Manager
Molecular Simulations Inc.
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