On compressibility under pressure coupling section of mdp

User discussions
1

GROMACS version: 2022
GROMACS modification: No

Dear GROMACS Users,

GROMACS is primarily used to simulate proteins in water solution. But if you wanted to simulate biomolecules in organic solvent, with pressure coupling on, several options are available. The one which seems relevant and has caught my eye is compressibility. By default, the value is 4.5e-5 which is for water and at 300K and 1 bar. How important is it that it must be changed to a value of a respective organic solvent which is used to simulate?

Thank you for any engagement with the topic.

Henry

2

Hi Henry,

As far as I understand: not so much. The compressibility always comes ‘in pair’ with the pressure coupling time. That is, the rate of rescaling (both Berendsen and C-rescale) is controlled by beta/tau_p. From the reference manual:

Here, β is the isothermal compressibility of the system. It suffices to take a rough estimate because the value of β only influences the non-critical time constant of the pressure relaxation without affecting the volume distribution itself.