Hello everybody,
Since few weeks I try to fix my simulation and I’m stacked.
SYSTEM:
Bulk of rigid CO2 molecules with temperature of 400K under pressure 250 bars with size around 118 x 118 x 118 A^3 (supercritical conditions). The system as whole is big in X direction (up to 10000A in both directions)(attached figure). The bulk is constrained by a LJ wall in positive X direction which prevent molecules to fly away behind certain region (purple one). On the other side of CO2 bulk I made a dense wall of carbon atoms. The piston is suppose to keep constant pressure when I remove the LJ wall from CO2 to let it defuse. So the piston should move slowly keeping the constant pressure of 250 bars no matter what I’m doing with CO2.
CODE:
units metal
boundary p p p
atom_style full
read_data system_plus_wall_38_atoms.data
timestep 0.001
#pair_style lj/cut/coul/long 8.775 10.0
#pair_coeff 2 2 0.00681 3.05 9.15
#pair_coeff 1 1 0.00233 2.80 8.40
#pair_coeff 1 2 0.00398 2.925 8.775
pair_style lj/cut/coul/long 10.0 10.0
pair_coeff 2 2 0.00681 3.05
pair_coeff 1 1 0.00233 2.80
pair_coeff 1 2 0.00398 2.925
pair_coeff 2 3 0.00398 2.925 3.283
pair_coeff 1 3 0.00233 2.80 3.143
pair_coeff 3 3 0.00233 2.80 3.143
kspace_style pppm 0.001
group O type 2
group C type 1
group CO2 type 1 2
group wall type 3
neighbor 2.0 bin
neigh_modify every 5 delay 10 check yes
compute Tr CO2 temp/com
compute Tp wall temp/com
fix right_cont_CO2 all wall/lj126 xhi 309.0 0.00398 2.925 3.2 units box pbc yes
fix NVT CO2 rigid/nvt/small molecule temp 400.0 400.0 0.4
fix PISTON wall rigid group 1 wall
velocity CO2 create 400.0 4928459 #zero angular
fix moving wall aveforce 2.2 0.0 0.0 #moving the system at certain direction
fix pNVE wall nve
The rest is dump and run commands.
PROBLEM:
I calculated with high attention the force I applied on piston which is 2.2 ev/A according to metal units. The piston is freezed due to the fix command. When I run the simulation (with optimized CO2 or not) the piston is pushing the gas really fast like there is no resistance and no pressure from CO2 molecules with LJ wall at the end of CO2 box or without. I simulated CO2 box separately and everything was fine about the pressure and equilibration went well. Could you tell me what can be wrong here? Or maybe I do not use a command as I should. I tried many option and non of them works well. I also was following all the pitson problems discussion and examples you gave but it doesn’t work for me.
Thank you in advance.
All the best,
Katarzyna Walczak.