The fluid flow of argon in a nanochannel with copper walls is simulated by molecular dynamics.
In this simulation, the lower copper wall is fixed and the upper copper wall moves at a fix rate. The temperature of the lower copper wall is 90K and the upper copper wall temperature is 190K and between the two walls liquid argon flows at temperature of 90K.
Argon-Argon and copper-Argon interactions is simulated by Lennard-Jones potential and EAM potential has been used for copper-copper interactions.
At the bottom of the lower fixed wall and above the movable upper wall, two fixed walls are simulated.
After applying the velocity and fixes of the groups of this couette flow, argon molecules diffuse into the copper plates.
If the timestep is too large then the argon can get into the copper during the timestep. Once in, there is no net force pushing it out.
You have to make sure no molecule can move more than one argon mean freepath in one timestep.
You have to give that repulse potential a chance to act on the argon.
Your temperature will let you estimate the molecule speed, V.
You can eyeball what the molecule seperation distance is, L.
So make timestep
Dear Saeed Assadi
It can have several reasons, some here are :
1- did you set the correct Copper lattice constant when you was making copper atomic arrangement.
2- Lennard-Jones interaction parameters for copper and argon , specially Sigme( σ ), may need modification; ( I think sigmeij should increases (i copper, j argon). If Lennard-Jones interaction parameter be wrong, atoms should become too close to repel force arise and prevent atoms to diffuse inside lattice. because argon atoms go through copper lattice, means copper doesn't act enough repel force on argon atoms to push them out.
3- Other possibility can be you set mass of copper or argon atoms too small or too big.
without raw file, these are my initial guesses.
Enjoy living in Guilan, I missed a lot of delicious food there.
If the timestep is too large then the argon can get into the copper during the timestep. Once in, there is no net force pushing it out.
You have to make sure no molecule can move more than one argon mean freepath in one timestep.
You have to give that repulse potential a chance to act on the argon.
Your temperature will let you estimate the molecule speed, V.
You can eyeball what the molecule seperation distance is, L.
So make timestep
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