[gmx-users] when using RB dihedral function, how to exclude 1-4 vdw ?

TJ Piggot t.piggot at bristol.ac.uk
Fri Nov 20 13:10:59 CET 2009

If you read this part of the manual again you will see that it discusses 
this point of 1-4 interactions for the OPLS forcefield and RB dihedrals 
(and the same as discussed for OPLS is true for the AMBER forcefields using 
RB  potentials for dihedrals).


--On Friday, November 20, 2009 16:45:44 +0800 XunJie Yang 
<yangxunj at mail.ustc.edu.cn> wrote:

> Hello GMX users:
>   I'm new to GMX and I'm now facing a problem. For short, it is about how
> to properly use the RB function.   I'm now doing simulation with AMBER
> force field(ported to GMX by FFAmber), which employs Ryckaert-Bellemans
> function for dihedral, it is how FFAmber forcefield treats dihedral
> angles as the parameters provided are only for RB function.    According
> to GMX Manual page 62, using RB function implies exclusion of 1-4 LJ
> interactions between the first and last atom of the dihedral, which
> means, I should turn off the 1-4 vdw term while retaining the 1-4 coulomb
> term. However, I haven't found the way of doing so. If I deleted the
> [pairs] block in the topology file, all 1-4 interactions including 1-4
> coulomb interaction would be deleted.   Could anyone who knows key to
> this problem give me some help? Thanks in advance!
> Yang Xunjie
> 2009-11-20
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TJ Piggot
t.piggot at bristol.ac.uk
University of Bristol, UK.

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