[lammps-users] about fix rigid!

Dear support,

my system is composed by
a) top rigid
b) bottom rigid
c) mobile atoms between top and bottom

The fix rigid command does not work as we want because it allow the rotation.

I want that the force on top and bottom are applied only at the center of the mass, so each atoms feel the same displacement and the rotation are not allowed.
Which is the better way to do this?

In my opininon the force between the mobile atoms and the rigid atoms are computed in two part:
a) the part relative to the mobile atoms are computed in the usual way
b) the part relative to the rigid atoms are computed by a variable that is equal and opposite to the sum of the external force on the mobile atoms

this kind of mechanism is already implemented in LAMMPS?

Best regard


Try the fix aveforce command.



the fix aveforce command apply an external force, in my case the external force is due to the atoms in the others groups.


2008/12/15 Steve Plimpton <[email protected]>

If you set the external force to 0.0 (not NULL) then the atoms
in the group will move in a rigid way due to being pushed
on only by other atoms. If you do this only in one dimension, then
the group would move up/down, for example. I think this
matches your description.