[gmx-users] p-coupling for inverted hexagonal phase

[Mohsen Ramezanpour]

Dear Gromacs users,

I am doing a simulation on inverted hexagonal (HII) phase composed of just
lipids and water.

(please have a look at HII phase here:
https://openi.nlm.nih.gov/detailedresult.php?img=PMC2695813_1757-5036-2-3-3&req=4
)

My question is regarding the pressure coupling for such systems. I am using
the anisotropic p-coupling at the moment:

pcoupl                 = Parrinello-Rahman        ; replaced
pcoupltype          = anisotropic
tau_p                  = 5.0
compressibility   = 4.5e-5  4.5e-5  4.5e-5  0 0 0
ref_p                   = 1.0     1.0     1.0     0 0 0

I think this is the correct way to treat this type of system.

Some might argue that a semi-isotropic p-coupling is the correct
treatment for that. i.e.

pcoupl                 = Parrinello-Rahman        ; replaced
pcoupltype          = anisotropic
tau_p                  = 5.0
compressibility   = 4.5e-5  4.5e-5
ref_p                   = 1.0     1.0

where the first is for Z (the cylindrical axis of HII phase) and the second
parameters control and scale the box size in both X and Y directions
equally.

I just like to know your opinions on this. Which one do you think is the
better way to treat such systems?

Thanks in advance for your comments.
Mohsen



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