 # Calculation of surface tension

GROMACS version: 2018
GROMACS modification: Yes with plumed

I want to calculate the surface tension of a liquid. For that I created a system and created an interface by extending the box length in the z-direction. After that I run an nvt simulation for 15 ns. Now I want to calculate the surface tension of the liquid, I used the gmx energy command but didn’t get anything useful. Can anybody guide me.

Thanks,
Devargya

Hi Devargya,

Did you use the surface-tension option for pressure coupling? It’s described here:

http://manual.gromacs.org/current/user-guide/mdp-options.html?highlight=surface%20tension

I assume you already stumbled upon this, but here is the section of the manual describing the surface tension algorithm

http://manual.gromacs.org/current/reference-manual/algorithms/molecular-dynamics.html?highlight=surface%20tension

I didn’t use the berendsen coupling. Somehow I skip the part that the surface tension option only works on that algorithm. I will try it again.

Thanks,
Devargya

Hi, Is it necessary to use surface tension coupling. I have seen papers where people have used `semi-isotropic` coupling and then calculated the surface tension. It must be wrong right?

Using gmx, I have calculated surface tension for the water-air surface. For an oplsaa forcefield, we obtained 57.9345 mN/m

After the NVT simulation, we performed an MD simulation using the following pressure and temperature coupling part. All other parts are the same.

; Temperature coupling is on
tcoupl = V-rescale
tc-grps = Water
tau_t = 0.5
ref_t = 300
; Pressure coupling is on
pcoupl = no
pcoupltype = semiisotropic
tau_p = 5.0
ref_p = 0.0 1.0
compressibility = 0.0 4.5e-5

You have no pressure coupling?

Yes, no pressure coupling.