Fixing the temperature of an oscillating wall

Hi,
I want to simulate an oscillating wall made of particles which will create a sound wave in the domain containing argon gas using LAMMPS. However, I want to thermostat the wall-particles as otherwise, it is giving rise to a heat flux to the argon gas particles in the domain.

I’m using fix_move wiggle to oscillate particles of the wall. On the top of it, I am using Berendsen (Not NVT as it will time integrate) thermostat to it. But it is not working and I’m unable to thermostat the wall particles.

Is it not possible simultaneously to oscillate the wall particles (using fix_move) and maintaining the temperature of the wall-particles using a thermostat (Berendsen or other thermostats other than NVT)?

Here is my test lammps- script. Right now, I just want to keep the temperature of the oscillating wall fixed. Is there a way to get it?

#-----------initialize simulation--------------
units metal
dimension 3
boundary p p m
atom_style sphere
atom_modify map array

#-----------create atoms--------------------

region box block -60.0 60.0 -60.0 60.0 -52.0 50.0
region inbox block -60.0 60.0 -60.0 60.0 -40.0 50.0
region wall block -60.0 60.0 -60.0 60.0 -52.0 -50.0
create_box 2 box
create_atoms 1 random 5000 125698 inbox
lattice fcc 3.0
create_atoms 2 region wall

fix walls all wall/reflect zlo -52.0 zhi 50.0 units box

#------M & D--------------------------------------------------

set type 1 mass 39.95
set type 1 diameter 3.4
set type 2 mass 40.078
set type 2 diameter 3.6

#-------------grouping-----------------------------------------------

group immobile region wall
group mobile subtract all immobile

set group mobile type 1
set group immobile type 2

---------- Define Interatomic Potential ---------------------

pair_style lj/cut 3.4
pair_coeff 1 1 0.0103 3.4 3.81
pair_modify shift yes
pair_coeff 2 2 0.2152 3.6 3.81
pair_modify shift yes
pair_coeff 1 2 0.0103 3.5 8.5
pair_modify shift yes
neighbor 6 multi
neigh_modify delay 10 check yes

----------------minimization of Ar---------------------

fix 1 immobile setforce 0.0 0.0 0.0
thermo 100
thermo_style custom step temp pe ke etotal press vol enthalpy
min_style cg
minimize 1e-25 1e-25 10000 1000000
unfix 1

#-----------------equilibration--------------------------------

timestep 0.001
velocity mobile create 300.0 123475 dist gaussian mom yes rot yes
fix 3 mobile nvt temp 300.0 300.0 0.01
fix 5 immobile move wiggle 0.0 0.0 3.0 0.5 units box
fix 7 immobile temp/berendsen 300.0 300.0 0.1
compute mytemp mobile temp
compute mytemp1 immobile temp
thermo 100
thermo_style custom step time c_mytemp c_mytemp1 pe ke etotal press vol
log lognew.txt
#----------------- Run-------------------

run_style verlet
run 1000000

Thanks & Regards,
Kanka

Hi,
I want to simulate an oscillating wall made of particles which will create
a sound wave in the domain containing argon gas using LAMMPS. However, I
want to thermostat the wall-particles as otherwise, it is giving rise to a
heat flux to the argon gas particles in the domain.

​you are not making much sense here. the heat exchange of gas atoms with a
wall due to thermal motions of the wall atoms is negligible compared to the
kinetic energy transferred due to your wall movements. ​

I'm using fix_move wiggle to oscillate particles of the wall. On the top
of it, I am using Berendsen (Not NVT as it will time integrate) thermostat
to it. But it is not working and I'm unable to thermostat the wall
particles.

​fix move completely ignores forces and velocities on atoms and just moves
them following a prescribed trajectory, so a thermostat fix *cannot* have
an impact.​

Is it not possible simultaneously to oscillate the wall particles (using
fix_move) and maintaining the temperature of the wall-particles using a
thermostat (Berendsen or other thermostats other than NVT)?

​first of all, the "wall temperature" is not a well defined concept here as
the wiggle oscillation are kinetic energy as well. so you have subtract
that bias out. or do the precribed motion in one direction and free time
integration and thermalization in the other two directions. this is all
very complicated and it is questionable whether this actually has a
meaningful impact.

axel.​