[lammps-users] A little difference between subsequent simulation using read_restart command

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1

Dear all,

I’ve encountered a problem.
I have a rigid layer of atoms in my system, on the right of the layer there are some molecules interacting with them, while on the left of which there is a constant force to every atom in the layer by using the command:
…
fix 1 slab rigid group 2 slab_1 slab_2 force * off off on
fix 2 slab_1 setforce 0 0 NULL
fix 3 slab_1 aveforce 0 0 0.05
…
Everything goes well in the calculation, by which I mean the layer only move in a rigid body in the z direction, and every atom in the layer have the same z coordination, then I write a restart file for later use.

But when I restart the file, (and of course using the fix rigid ,setforce and aveforce), in the first frame all the atoms have the same z coordination while, as the simulation proceeds their z coordination become different, does that mean either they are not moving as a rigid body or there are force not in the z direction.

I tried to use restart2data tool to make a data file and avoid using read_restart command, but when I read the data file generated and start, nothing happened, only on screen:

2

The restart file stores nothing about these fixes, so I don't know
why you wouldn't be able to run the same problem after restarting.
I will mention that you don't need to use a fix rigid command. If
you slab just moves as you describe, then the other 2 fixes
are sufficient.

Steve

3

Dear Steve,

Now I can successfully restart the calculation and by changing

“fix 1 slab rigid group 2 slab_1 slab_2 force * off off on”

into
“fix 1 slab rigid group 2 slab_1 slab_2 force * off off on torque * off off off”
I don’t know why there are these torques, since they were not exist before the former simulation.

But when I follow your suggestions and tun off the fix rigid command,
I found that the layer of atoms does not move any more,
as if it is a wall standing still there.

I don’t know why!

Chen Chen