coul-lambda affects the pressure computation of a ligand with zero partial charge
This is a simplified and corrected version of the issue 2600.
I'm trying to compute the decoupling free energy of vdw interactions of a ligand which has zero partial changes.
Since the ligand has zero partial, changing coul-lambda shouldn't have any effect on anything.
However, setting coul-lambda to 0 yields a pressure 2.13121e+02 bar of whereas setting coul-lambda to 1 yeilds a pressure of 1.07168e+02 bar.
The commands to reproduce the results are
gmx grompp -f coul-lambdas_0.mdp -c prod.gro -o coul-lambdas_0.tpr
gmx mdrun -deffnm coul-lambdas_0 -rerun prod.gro
gmx grompp -f coul-lambdas_1.mdp -c prod.gro -o coul-lambdas_1.tpr
gmx mdrun -deffnm coul-lambdas_1 -rerun prod.gro
If you compare the pressure in coul-lambdas_1.edr and coul-lambdas_0.edr, you will notice that the pressure are different whereas they should be the same.
#4 Updated by Berk Hess about 1 year ago
- Status changed from Accepted to Fix uploaded
- Assignee set to Berk Hess
The Coulomb forces were, incorrectly, scaled with lambda.
This bug (only) occurs when no charges are actually perturbed. Or, analogously, for LJ-PME when no atom types are actually perturbed.