No, the point is that the equilibrium surface area is near zero in the context of PBC and you need
special tricks to keep the system away from that equilibrium. There will always be a force toward reducing the surface area of the hydrophobic/hydrophilic interface. It is possible to disallow this force to cause system relaxation by using an incompressible Cartesian z (or x and y), but as soon as you let that go the system will then relax toward the tall and thin column of aliphatic chains. Perhaps you should return to the list with a detailed description of what you are trying to accomplish and you might get some help. I doubt that I can help that part, but there is likely somebody out there who can. Also, you will increase your chances of getting help from somebody like me (expert gromacs user who is totally ignorant of your particular field of study) by giving proper explanations of thing like the "interfacial tension of surfactant at oil/water interface". I know that it makes sense to you (and probably lots of other people), but I for one don't know exactly what you are trying to accomplish. Chris. -- original message -- Dear Chris: Thank you for your help. Maybe I can try it as this. First set x and y fixed by setting compressibility = 0 4.5e-0.5 until the system reaching equilibrium and then release. If it sounds reasonable. I am trying to do it. Dear Hugh:
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