In solvation free energy simulations with **gmx 2020.1** the vdW component of dG and DHDL is **~2X overestimated** at the lambda region in which vdw-lambdas are changing. Additional testing has shown that this issue is related to "**vdw-type = PME**". I have compared (for lambda-state=4) <dVvdw/dl> results of **gmx2020** with vdw-type: **PME** and **CutOff**, with the result of old **gmx5.1** with vdw-type = PME. All was run on CPU for 5 nanosecs with **PME electrostatics**. It turned out that **gmx2020** with **vdw-type=CutOff** reproduces (within the accuracy) the <dVvdw/dl> result of **gmx5.1** with **vdw-type = PME**, which is expected. In the uniform environment both vdw-types should give accurate solvation FE. The result of **gmx2020** with **vdw-type=PME**, however, is around 2X exaggerated, which seems to be a bug. Here are the numbers: | gmx-ver/vdw-type | <dVcoul/dl> | <dVvdw/dl> | | ------ | ------ | ------ | | 2020/PME | -6.39450e-01 | 9.72647e+01 | | 2020/CutOff | -3.99985e-01 | 4.39876e+01 | | 5.1/PME | -3.08675e-01 | 4.36738e+01 | Note, the problem is related to **DHDL only**, all potential energy components (including vdW) in all runs are consistent. Test files are in the attached archive [test_solvation.tar.gz](/uploads/33ce1ca6b088cf05c029445c0ca99afa/test_solvation.tar.gz). Compare log in lambda.04 folder.