How to confine argon particles in a T-region with periodic boundary conditions Yahoo / Sent

Dear Lammps Users,

I am trying to simulate the evaporation of liquid argon between copper walls. My question is that how I can confine the argon particles in a T-region. I have attached the figure of the computational domain to this email.

I actually used “dynamic group” for vapor argon group and “fix wall/reflect” for the boundaries of the vapor region but I received an error that the fix does not allow use of dynamic group.

Any other idea that can also satisfy the periodic boundary condition?

Many thanks in advance!