Archive from user: zhiyi wu 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. *(from redmine: issue id 2640, created on 2018-09-07 by gmxdefault, closed on 2018-09-27)* * Relations: * relates #2849 * Changesets: * Revision 12f01f7917dec5863bf76437fc470bc3b45484b2 by Berk Hess on 2018-09-10T19:55:39Z: ``` Fix PME forces with FE without perturbed q/LJ PME would incorrectly scale the mesh forces with lambda when no charges or LJ atom types were actually perturbed. Fixes #2640 Change-Id: I193d55cf76d842f5b04d3a220411282c06b08a90 ``` * Revision a507acbc77fd61903c0fb685bba152ce613a6a0b by Berk Hess on 2020-02-04T10:05:04Z: ``` Actually fix PME forces with FE without perturbed q/LJ PME would incorrectly ignore the mesh forces on perturbed atoms when no charges or LJ atom types were actually perturbed. This is because the "fix" in commit 12f01f79 incorrectly changed the lambda value used for the PME forces from the actual lambda value to 1 instead of to 0 as it should have been. Fixes #2640 Fixes #3359 Change-Id: Ib19565bf017ddbd2fddc66c52be0ff9efc7e707c ``` * Revision 7387a098731a9b51f9f05c6d62059ee6d726358d by Berk Hess on 2020-02-05T07:14:49Z: ``` Actually fix PME forces with FE without perturbed q/LJ PME would incorrectly ignore the mesh forces on perturbed atoms when no charges or LJ atom types were actually perturbed. This is because the "fix" in commit 12f01f79 incorrectly changed the lambda value used for the PME forces from the actual lambda value to 1 instead of to 0 as it should have been. Fixes #2640 Fixes #3359 Change-Id: Ib19565bf017ddbd2fddc66c52be0ff9efc7e707c ``` * Uploads: * [pressure.tgz](/uploads/abab8b73bf009164c9ff274b70d1c326/pressure.tgz)