Hello,

I have a coarse grained (Martini) system containing a DPPC bilayer and DPPC spherical vesicle, and I want to study surface tension induced fusion between the two. I want to apply constant surface tension in the lipid bilayer, which I think can be done by pressure_coupling "surface-tension" in gromacs software. In the discription of the mdp options it's written:

The first ref-p value is the reference surface tension times the number of surfaces [bar nm], the second value is the reference z-pressure [bar].

what would be the value of no. of surfaces in my system? And will the surface tension be also applied to the spherical vesicle?

I would appreciate some help!