# Is gmx bar reading dH/dl for masses?

**URL:** <https://gromacs.bioexcel.eu/t/is-gmx-bar-reading-dh-dl-for-masses/10316>\
**Category:** User discussions\
**Tags:** free-energy\
**Created:** [October 10, 2024, 1:36pm UTC](https://gromacs.bioexcel.eu/t/is-gmx-bar-reading-dh-dl-for-masses/10316 "2024-10-10T13:36:45Z")\
**Posts on this page:** 1\
**Showing post:** 9

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**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:** [October 15, 2024, 4:15pm UTC](https://gromacs.bioexcel.eu/t/is-gmx-bar-reading-dh-dl-for-masses/10316/9 "2024-10-15T16:15:07Z")

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Ah, I see the issue now. I was looking at dH/dlambda, as in the title of your post, that is present. But the foreign lambda terms are all zero and that is what gmx bar uses.

I filed an issue: [Foreign Hamiltonian differences for perturbed masses are zero (#5195) · Issues · GROMACS / GROMACS · GitLab](https://gitlab.com/gromacs/gromacs/-/issues/5195)  
And I uploaded a fix: [Draft: Add effect of perturbed masses to foreign Hamiltonian differences (!4661) · Merge requests · GROMACS / GROMACS · GitLab](https://gitlab.com/gromacs/gromacs/-/merge_requests/4661)

Thanks for reporting this.

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