AMBER Archive (2006)

Subject: RE: AMBER: problem in saving parameter file for non-standard residue

From: Ross Walker (ross_at_rosswalker.co.uk)
Date: Fri Jan 13 2006 - 10:49:17 CST


Dear Priti,

> Could not find bond parameter for: C - sh
> Could not find bond parameter for: o - N
> Building angle parameters.
> Could not find angle parameter: O - C - sh
> Could not find angle parameter: C - sh - hs
> Could not find angle parameter: C - sh - c3
> Could not find angle parameter: CT - C - sh
> Could not find angle parameter: o - N - H
> Could not find angle parameter: o - N - CT
> Could not find angle parameter: c1 - o - N
> Building proper torsion parameters.
> ** No torsion terms for O-C-sh-hs
> ** No torsion terms for O-C-sh-c3
> ** No torsion terms for CT-C-sh-hs
> ** No torsion terms for CT-C-sh-c3
> ** No torsion terms for c1-o-N-H
> ** No torsion terms for c1-o-N-CT
> ** No torsion terms for c3-c1-o-N

Building parameters from scratch is hard work and requires a lot of fitting
to quantum and experimental data. As a first approximation however, for the
missing GAFF to FFXX parameters I would obtain the GAFF force field paper
and then see if you can find similar parameters.

E.g. for
C-sh

I would look at what Gaff would give for the following system:

    O
    ||
CH3-C-S-H

Then add that to an frcmod file as the type C-sh.

If the parameters are missing from the GAFF force field you could always
build a suitable 'model' compound of the connection region and run it
through antechamber to see if it will interpolate parameters for you.

This will be a reasonable guess at the parameters that you can always tweak
later.

I hope this helps.
All the best
Ross

/\
\/
|\oss Walker

| Department of Molecular Biology TPC15 |
| The Scripps Research Institute |
| Tel: +1 858 784 8889 | EMail:- ross_at_rosswalker.co.uk |
| http://www.rosswalker.co.uk | PGP Key available on request |

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