[gmx-users] force on protein by solvent

[SebastianWaltz]

Dear all,

I want to calculate the force on each protein atom induced by the SPC
solvent. Therefore I use the mdrun -rerun option and add to the .mdp
file the line
 energygrps          =  Protein SOL
If I compare afterwards the total force and the force of the solvent
written to the trr file I get for the second one absolute values which
are up to two times bigger when the total forces (including all the
protein protein forces). I do not think that cancellations of inter and
intra molecular forces should have such a big impact. Without the
energygrps the rerun gives the same values as the original run.
So I am not sure if it is enough to just add the above line to the .mdp
file before doing the restart.

Any help is welcomed

Thanks


Basti