# Abnormal dVremain/dl values in GROMACS 2025.0 with vdw-type=pme and free-energy

**URL:** <https://gromacs.bioexcel.eu/t/abnormal-dvremain-dl-values-in-gromacs-2025-0-with-vdw-type-pme-and-free-energy/13344>\
**Category:** User discussions\
**Tags:** mdp-parameters, mdrun\
**Created:** [March 30, 2026, 1:57pm UTC](https://gromacs.bioexcel.eu/t/abnormal-dvremain-dl-values-in-gromacs-2025-0-with-vdw-type-pme-and-free-energy/13344 "2026-03-30T13:57:25Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![donghwanz](https://avatars.discourse-cdn.com/v4/letter/d/97f17d/32.png) [@donghwanz](https://gromacs.bioexcel.eu/u/donghwanz)\
**Post date:** [March 30, 2026, 1:57pm UTC](https://gromacs.bioexcel.eu/t/abnormal-dvremain-dl-values-in-gromacs-2025-0-with-vdw-type-pme-and-free-energy/13344/1 "2026-03-30T13:57:25Z")

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GROMACS version: 2025.0 (bug) / 2024.4 (normal)  
GROMACS modification: No

I found a potential bug in GROMACS 2025.0 related to  
free energy calculations with LJ-PME (vdw-type=pme).

Symptom:

- GROMACS 2024.4: dVremain/dl ~ -700 kJ/mol (normal)
- GROMACS 2025.0: dVremain/dl ~ 5×10²² kJ/mol (abnormal)

Key MDP settings:

- vdw-type = pme
- free-energy = yes
- couple-lambda0 = none
- couple-lambda1 = vdw-q
- couple-intramol = no
- sc-alpha = 0.5

Full MDP:

integrator = md  
nsteps = 200000  
dt = 0.002  
cutoff-scheme = Verlet  
rlist = 2.0  
verlet-buffer-tolerance = -1  
coulombtype = pme  
rcoulomb = 1.2  
vdw-type = pme  
rvdw = 1.2  
dispcorr = no  
constraints = all-bonds  
lincs-order = 12  
tcoupl = v-rescale  
tc-grps = system  
tau-t = 0.2  
ref-t = 310  
pcoupl = parrinello-rahman  
ref-p = 1  
compressibility = 4.5e-5  
tau-p = 5  
free-energy = yes  
couple-moltype = MOLTYPE  
couple-lambda0 = none  
couple-lambda1 = vdw-q  
couple-intramol = no  
init-lambda-state = LAMBDA  
fep-lambdas = 0.0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4  
0.45 0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85  
0.9 0.95 1.0  
sc-alpha = 0.5  
sc-power = 1  
sc-sigma = 0.3  
sc-coul = yes  
calc-lambda-neighbors = 1  
nstdhdl = 50

Is this a known bug in 2025.0?  
Does anyone have a workaround?

Thank you.

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<div class="post-metadata">

**Author:** ![hess](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/hess/32/416_2.png) [@hess](https://gromacs.bioexcel.eu/u/hess)\
**Post date:** [March 30, 2026, 3:06pm UTC](https://gromacs.bioexcel.eu/t/abnormal-dvremain-dl-values-in-gromacs-2025-0-with-vdw-type-pme-and-free-energy/13344/2 "2026-03-30T15:06:24Z")

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No, this is not a known issue.

At which lambda(s) does this occur? Are you using GPUs?

Have you tried 2025.4 and/or 2026.1?

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<div class="post-metadata">

**Author:** ![donghwanz](https://avatars.discourse-cdn.com/v4/letter/d/97f17d/32.png) [@donghwanz](https://gromacs.bioexcel.eu/u/donghwanz)\
**Post date:** [March 30, 2026, 11:03pm UTC](https://gromacs.bioexcel.eu/t/abnormal-dvremain-dl-values-in-gromacs-2025-0-with-vdw-type-pme-and-free-energy/13344/3 "2026-03-30T23:03:08Z")

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Thank you for your response.

This occurs at all lambda windows (lambda 0 to 20).

Regarding GPU: Yes, we are using NVIDIA GPUs.

Regarding newer versions:

- GROMACS 2024.4: dVremain/dl ~ -700 kJ/mol (normal)
- GROMACS 2025.0: dVremain/dl ~ 5×10²² kJ/mol (abnormal)
- GROMACS 2025.4: dVremain/dl ~ 5×10²² kJ/mol (abnormal)

We have not tested 2026.1 yet.

Is this bug present in 2026.1 as well?  
Any workaround would be appreciated.

Thank you.

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<div class="post-metadata">

**Author:** ![hess](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/hess/32/416_2.png) [@hess](https://gromacs.bioexcel.eu/u/hess)\
**Post date:** [March 31, 2026, 6:39am UTC](https://gromacs.bioexcel.eu/t/abnormal-dvremain-dl-values-in-gromacs-2025-0-with-vdw-type-pme-and-free-energy/13344/4 "2026-03-31T06:39:16Z")

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I have no clue what could be wrong here. I don’t see any changes in the free-energy code between the 2024 and 2025 releases. Could you run one lambda value simulation with -nb cpu to check if this is GPU related?