Simulation of Water Flowing Through a Membrane

Dear all lammps user,

I have been trying to simulate desalination of seawater using graphene sheet as its membrane. The water on both side of reservoirs are pushed using another graphene wall acting as a piston.
I use the fix setforce to make the membrane fixed at its place and I use the fix aveforce to move the pistons.
The problem I met is there’s no water molecules passed the membrane. I thought that it’s normal, but it happened even when the pressure difference is 600 bar.

To set the pressure in the high pressure feed side, I take a number say it 120, I assume the pressure unit is bar. Then I put this number as a variable, to make it into force, I convert the value of 1 bar into Kcal/mol.A (unit for force in lammps real units). The graphene piston consists of 416 atoms with area of 1081.6 A, so I divided the converted value of pressure (bar) with 416. I highlight those converted value in this email. In my opinion, my problem with no water molecules to pass the membrane is connected with the force, but I cannot find what is wrong. Any idea or is there any unsuitable in my script?
Thank you.

Here is my input script:

You can monitor the pressure of a reservoir on one side

of the membrane that you are pushing on with the piston.

By using compute atom/stress for those atoms. I also

suggest you start with a “membrane” that has large holes

and verify that you can push water thru it. Then start shrinking

the holes until you get to the membrane geometry you want.

In other words, “debug” your input script by running simpler

simulations you can verify work, then add complexity.

Steve