Help regarding use of NPT fix

Hi all!!

I am new to LAMMPS so please excuse me if my questions are trivial.

I am simulating osmotic flow of salt solution through a CNT. My system consists of a pure water region on one side and a salt solution region on the other side. Two membranes of graphene with holes are connected by a CNT and sandwiched between the water and solution region.

I want to ensure that both the water region and the salt solution region are at the same temperature and pressure (300 K , 1 atm) before the actual dynamics start.

  1. As such during the equilibration stage, should I use two different npt fixes for the two different region to bring them to the same pressure and temperature.
  2. If so, how to define the pressure for the two different regions to be used by the npt fixes as the pressure is computed for all the atoms in the system rather than a specific region.

Note : The geometry and input files are attached.

Regards,

Manash

geometry.data (610 KB)

input.in (4.38 KB)

Hi all!!
I am new to LAMMPS so please excuse me if my questions are trivial.

I am simulating osmotic flow of salt solution through a CNT. My system consists of a pure water region on one side and a salt solution region on the other side. Two membranes of graphene with holes are connected by a CNT and sandwiched between the water and solution region.

I want to ensure that both the water region and the salt solution region are at the same temperature and pressure (300 K , 1 atm) before the actual dynamics start.

  1. As such during the equilibration stage, should I use two different npt fixes for the two different region to bring them to the same pressure and temperature.

No.

  1. If so, how to define the pressure for the two different regions to be used by the npt fixes as the pressure is computed for all the atoms in the system rather than a specific region.

You shouldn’t use fix npt at all. As you have a slab system, pressure will relax automatically. Using reflecting walls is pointless for this setup, since atoms must not come even near the box boundaries for the poisson solver to work correctly.

Since you say that you are new to lammps, I strongly recommend that you start with simulations of simpler systems before working on such a complex setup. You also need to spend some time understanding the physical underpinnings of the features you use, or you will have quite a bit of frustration or even ridicule ahead of you.

Axel

Thank you sir for your reply. As suggested, I shall first start simulations for simpler systems.

Regards,
Manash