[gmx-developers] Incorrectly large pressures at lambda=1 with perturbed masses

[Bert de Groot]

Hi Jochen,

sounds as if this could be related to 
https://gitlab.com/gromacs/gromacs/-/issues/3943

which was fixed only very recently:

https://gitlab.com/gromacs/gromacs/-/merge_requests/1197

could you perhaps test if that fixes your issue as well?

cheers

Bert


On 3/2/21 9:35 AM, Jochen Hub wrote:
> Dear Gromacs developers,
>
> we get incorrectly large pressures in FEP simulations in the lambda=1 
> state if we perturb the masses of all hydrogen atoms. Specifically, we 
> simulate a pure-water box and perturb the masses of all H atoms from 
> 1amu to 2amu. This happens with Gromacs 2019.6, 2020.5, and 2021, but 
> NOT with 2018.6.
>
> The pressures are shown in a PDF here:
>
> https://cloud.hiz-saarland.de/s/NH6Mz8QKi39qBH7
>
> (The relaxation in the problematic cases is due to rapid box expansion).
>
> We have a test system here:
>
> https://cloud.hiz-saarland.de/s/o2j7K4GK7wojayi
>
> This does NOT happen if:
>
> - masses are not perturbed
> - using Gromacs 2018.6
> - the same state is defined to lambda=0 by modifying the topology
>
> To us, this looks like a potentially severe bug which was not detected 
> because we typically perturb only few atoms and not 2/3 of the all 
> atoms, as we do here.
>
> Is this issue known?
>
> Best wishes,
> Johanna and Jochen
>
>