Hi everyone,

I know that using the constant potential method (CONP) https://github.com/zhenxingwang/lammps-conp#:~:text=Constant%20potential%20method%20is%20an,fluctuations%20in%20the%20electrolyte%20solution.

you can explicitly define the potential but it seems I cannot use it with GPUs and I want to either use the “fix efield” command or define opposite charges on my electrodes.

Here is the system I want to study:

I have two graphene electrodes, 6A * 6A (1500 atoms each), that they are separated by 100A from each other (in the z-direction), my solvent is water and I have two different ions inside that.

Now the question is if I assign a specific charge to each carbon atom of graphene, let say 0.05e and -0.05e for positive and negative sheets, how can I calculate the applied voltage between the two electrodes?

Is that true if I calculate E (electrical field) using “surface charge density” and divide it by the “relative permittivity”, not sure if I have to use this or something else. but I do not know how to obtain surface charge density? are you just obtaining the surface by multiplying the dimension of the graphene, like here 6 *6 A2, or do you need to calculate the surface of each carbon atom?

Second method: can I use the “fix efield” command in the z-direction? If Yes, how can I use it to have let say 2V between my two electrodes?

fix 5 gra efield 0.0 0.0 0.02

because if I use V = Ed, where E is in V/A ==> V = 0.02 * 100 = 2 V

But this one does not make sense for me, because I am applying a field on the graphene how does it affect the solvent and ions inside it?

I really appreciate your comments