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[lammps-users] Fixing the temperature of an oscillating wall
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[lammps-users] Fixing the temperature of an oscillating wall


From: Kanka Ghosh <kanka.kankaghosh.ghosh@...24...>
Date: Sat, 26 May 2018 21:58:41 +0530

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
--
Kanka Ghosh
Senior Research Fellow
Dept.of Physics
HSB-209A
IIT Madras
India