[gmx-users] R-B dihedrals

[Alex]

I have a set of dihedrals described by the R-B potential, with a minimum at
90 degrees, and minimization indeed yielded angles very close to that.

At some point, I decided to check if I can rotate the groups to another
angle, say, 45 degrees. Simple enough, so I changed the expression. Energy
minimization shows no difference -- still 90 deg. I turned off vdw for all
atoms in the vicinity, set all charges to zero -- no difference. Hiked up
the dihedral constant by three(!) orders of magnitude -- nothing.
Commenting out these dihedrals immediately causes grompp errors, so they
are definitely seen by the system (I tracked the errors to the atomtypes).
The dihedral type (3) is listed correctly in the topology. A David Lynch
mystery.

Any ideas?

Thanks,

Alex