Fix wall/region

Hi everyone,

  I am using the wall/region fix with a shape of a cylinder. Sadly, lammps
is complaining about atoms on or inside the region assigned. I already
performed a delete_atoms to check if there are atoms inside the cylinder
and no atoms were deleted. What seems to be the problem? I also reduced
the cutoff for the harmonic wall with no success.

  Using 19-jul version and gpu acceleration.

  Thanks in advance!

  Best,
  Luis

If you want the wall to contain atoms so they remain
inside the cylinder, then the error is b/c you have atoms
outside the cylinder, i.e. they are "inside" the wall
that is trying to contain them.

Steve

No, I want the wall without atoms inside. Then I will move the wall
towards a group of atoms to simulate an indentation.

In this case, I have to use 'side in' for the region, with no atoms
inside. Is that it?

  Luis

The confusion here is about inside/outside.
I assume you want to run a simulation with
atoms inside a cylinder and use a cylindrical
region as a wall to contain the atoms. In that
case you need to start with all your atoms
truly inside the cylinder (can't be outside and
can't even be on the surface of the cylinder).

If the wall fix complains about atoms being
"inside the wall" at some point (either at
the start or after running dynamics), it means
they have moved "outside" the cylinder,
which is illegal. Conversely, when atoms
are "inside" the cylinder they are "outside"
the wall, so that the wall can continue to
push on them.

Steve

My goal is to create a cylinder with no atoms inside (there is vacuum for
it). This cylinder will be moved towards a group of atoms that were
initially outside the cylinder. With this setup I intend to make this
cylinder-shaped wall as an indenter. Therefore, I want the cylinder to
push away atoms in its trajectory.

That being said, which option should I use to create the region: side in
or out? Is the harmonic wall the most suitable for this case?

BTW, is this setup feasible in Lammps?

Luis

My goal is to create a cylinder with no atoms inside (there is vacuum for
it). This cylinder will be moved towards a group of atoms that were
initially outside the cylinder. With this setup I intend to make this
cylinder-shaped wall as an indenter. Therefore, I want the cylinder to
push away atoms in its trajectory.

That being said, which option should I use to create the region: side in
or out? Is the harmonic wall the most suitable for this case?

how about using fix indent with the cylinder option?

axel.

I thought about it but I want to indent with the base of the cylinder.

Actually I want a flat circular indenter.

Luis

To do this you want to define the region with "side out"
and invert everything I said in my previous email. It should
work fine.

Steve

Ok, it's working now! Thanks

Luis