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

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!



Dear Axel and Users,
I am getting an error when I run my gcmc simulation. in case of molecular template command like offset. I give a brief view of my file set up in input script below

units real
dimension 3
boundary p p p
atom_style full
atom_modify map array
pair_style lj/cut 12.5

variable a loop 8
variable p index 0.8 0.85 0.9 0.95 1.0 1.05 1.1 1.15

molecule gas gas1.molecule offset 4 0 0 0 0 # molecule templates


log log Cu_D_$a

molecule gas gas2.molecule # molecule templates

molecule gas gas2.molecule 4 0 0 0 0 # molecule templates

Define interatomic potential

pair_style lj/cut 12.5
pair_coeff 1 5 0.0664 3.1275 #Ni
pair_coeff 3 5 0.16771 3.3815 #O
pair_coeff 2 5 0.16718 3.6015 #C
pair_coeff 4 5 0.06684 3.288 #H
pair_coeff 5 * 0.053649 2.8 #gas
pair_coeff 6 * 0.156973 3.05

Define groups fixes computes (see LAMMPS manual)

group gas type 5 6
group sol type 1 2 3 4

neigh_modify exclude molecule sol

neigh_modify exclude molecule gas

fix 1 all rig nvt temp 298 2 0

fix 2 gas gcmc 1 1000 1000 0 3366593 298.0 -0.5 0.1 mol gas pressure $p fugacity_coeff 1

fix 1 gas gcmc 100 10 10 0 34565 300.0 -0.5 0.1 maxangle 10.0 mol gas

Simulation data output and dump options

compute_modify thermo_temp dynamic yes
log Cu_DO_$a

thermo 10
thermo_style custom step atoms vol cella cellb cellc cellalpha cellbeta cellgamma
dump 2 all custom 1 dump_all id type x y z

dump m1 all image 1 all*.jpg type type view 0.0 45

dump aa gas image 5 gas.*.jpg type type

Not clear on why you need a dynamic group. But I don’t
think there is a conceptual problem with allowing fix wall/reflect
to use a dynamic group. Axel can comment. If it’s OK,
he can make the simple code change to enable it I GHub,
so that is is soon added to LAMMPS.


walls for standard point particle interactions, which includes fix
wall/reflect, are fine with dynamic groups, since there are no checks
and other requirements. i've just added the suitable changes to a
pending pull request. this change should be included in the next
LAMMPS patch.