[gmx-users] Pressure control with constraints incompatible with expanded ensemble

[Jacob Monroe]

Hi all,

I would like to use Gromacs (2018 versions on GPUs) to compute solvation free energies using expanded ensemble simulations.  I have no problems in the NVT ensemble, but when I try and implement pressure control I run into errors.

Specifically, if I want to use expanded ensemble, I must use the md-vv integrator.  If I use this integrator, I must select MTTK pressure control (I’d rather not use Berendsen for production runs), but if I want to constrain hydrogen bonds, I cannot use MTTK (grompp throws an error).  Previous versions of Gromacs appear to have allowed MTTK as long as SHAKE was used for constraints (see the mdp files here: http://www.alchemistry.org/wiki/GROMACS_4.6_example:_Ethanol_solvation_with_expanded_ensemble).

So is the only way to run NPT, expanded ensemble simulations with current versions of Gromacs to use the Berendsen barostat?

Thanks,
Jacob