[gmx-users] Change of force field: ffgmx > ff53a5

[Justin A. Lemkul]

Thomas Schlesier wrote:
> Dear all,
> i want to ask if the following way to change the used force field for a
> molecule is right.
> I used PRODRG to get a topologie for my molecule, so i have it with the
> ffgmx force field. My idea is to simply change the parameters. If i have
> for example a N-H bond i would use the parameter from ffG53a5bon.itp. I
> think i must also change the names of the atom types (use CH2R for CR61;
> from xyz.atp)? When also this is done i have the topologie for the
> ff53a5 force field, or have i overlooked something?

In theory, yes, using the skeleton topology from PRODRG will work fine, if you 
change all of the parameters that differ between ffgmx and ffG53a5.  I am not 
100% sure about differences in bonded parameters between ffgmx and ffG53a5, so 
this next point may or may not matter.  You can use PRODRG2.5 (aka PRODRG beta) 
to generate an ffG43a1-compatible topology.  The bonded parameters between 
ffG43a1 and ffG53a5 did not change, so you save yourself a lot of needless 
correction, if indeed there were changes to the ffgmx and ffG53a5 bonded parameters.

Otherwise, yes, I'd say your approach is a reasonable starting point.

-Justin

> Thanks for an answer
> Thomas
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-- 
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Justin A. Lemkul
Graduate Research Assistant
Department of Biochemistry
Virginia Tech
Blacksburg, VA
jalemkul[at]vt.edu | (540) 231-9080
http://www.bevanlab.biochem.vt.edu/Pages/Personal/justin

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