[gmx-users] Surface tension for membrane simulation

[Xiang Ning]

Hi all,

I have a question of surface tension in membrane simulation. I found that in equilibration and production step, the pressure set up for membrane simulation is below:

; Pressure coupling is on
pcoupl          = Parrinello-Rahman         ; Pressure coupling on in NPT
pcoupltype      = semiisotropic             ; uniform scaling of x-y box vectors, independent z
tau_p           = 2.0                           ; time constant, in ps
ref_p           = 1.0   1.0                     ; reference pressure, x-y, z (in bar)
compressibility = 4.5e-5        4.5e-5  ; isothermal compressibility, bar^-1
 
I would like to know, during these steps, do we have constant pressure or constant surface tension? Moreover, different membrane have different surface tension, do we need to change and write it in the mdp file (ref_p value?) to run the simulation? 

Thanks a lot for your assistance! 

Best,
Ning