Re: [AMBER-Developers] [AMBER] ATTN GLYCAM users: CY atom type work around

From: Yong Duan <>
Date: Sun, 11 Dec 2011 15:16:26 -0800

A list of atom types is easy to generate. In any case, there was not much
coordination before. We definitely need to improve.

Did you notice CY being used anywhere else? I noticed it is in
opls_parm.dat (for heme).

If you ask me, I think, in general, we should try to avoid redefining
existing atom types. Or, we'd expect conflict somewhere.

Yong Duan, Ph.D, Professor
UC Davis Genome Center and
Department of Biomedical Engineering
University of California at Davis
Davis, CA 95616
On 12/11/11 3:03 PM, "B. Lachele Foley" <> wrote:
>I would still argue for a list because it will help people who are trying
>to decide which force fields can be used together.  Since the Leap's
>don't complain if something is multiply defined, it becomes easy for
>parameters to silently be mis-loaded.  And, while you can say "the user
>needs to learn to go look in the files," it seems we could make that a
>little easier.  For example, if one merely looks at the defs at the top
>of parm94.dat, you would think CY isn't being used.  And, it isn't --
>except for a van der Waals-type equivalence near the bottom.
>Perhaps CY wasn't a great choice, but it seemed as if parm91 was merely
>claiming it for some future use (as carbon-13, apparently), and its use
>had been mostly dropped by 94.  In 94, its remaining as a vdW equivalent
>was probably just an oversight.  So, it wasn't being used anymore, as far
>as we knew.  
>What I'm saying is that if an atom type is used in something so old it's
>been hidden down in "oldff", should we still worry about reusing it?  In
>04, the CY type hadn't been written significantly into a "parm" force
>field in 13 years.  Maybe we shouldn't ever reuse, but there are only so
>many 2-letter combinations.
>We can't just load glycam as a frcmod afterwards.  The trouble is that
>the definitions are too different.  Our CY is sp3, and others are sp2.
>So, we have to load our atom types, then their atom types, then their
>parameters, then our parameters.
>:-) Lachele
>Dr. B. Lachele Foley
>Complex Carbohydrate Research Center
>The University of Georgia
>Athens, GA USA
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Received on Sun Dec 11 2011 - 15:30:03 PST
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