Issue with Wall movement.

Dear Steve, Users,

I am having issues with moving my wall (that I need for my simulations).

First, I want to create two seperate walls from two block like
regions. Then, I want to keep one of those walls fixed and other
moving during the course of the simulation in certain direction. Below
is my sample input script with comments which I wrote based on my
understanding from the manual.

I have 5 type of atoms in my simulation, type 1 and type 2 are
supposed to be 2 seperate walls. These are essentially Si slabs in X-Y
plane. Type 1 is bottom layer (group Sib) which should be fixed. Type
2 is top layer (group Sit) which I am planning to move. But with this
script, what I see is that the top wall does not move at all.
I will highly appreciate anybody's input.

Defining a region that moves has nothing to do with atoms.
A region is simple a geometric portion of 3d space. if a region
"moves", nothing will cause the atoms inside it to move as well.

I think you want the fix move command.


Dear Steve,

Thanks for the email. I think what you are saying is correct. I should
have seen it, myself. Actually, when I was going through fix
wall/region command, I misinterpreted the following lines.

"Regions can also change over time via keywords like linear, wiggle,
and rotate, which when used with this fix, have the effect of moving
the region surface in a prescribed manner. "

I thought that when the regions move (in a prescribed manner), atoms
will also move. Now you mentioned, I think the purpose of fix
wall/region command is to create some empty regions and move the
region as a barrier to other atoms. Please let me know that if makes
sense. If not, where we could use this command.

I will give fix move a shot and it should work out.

Best Regards,

You can use fix wall/region with a dynamic (moving)
region and the atoms will feel the effect of the moving
surface of the region (e.g. be repulsed by it).

But if all you want to do is move a chunk of atoms
as a rigid chunk, I would use fix move.