I want to calculate the torque on a group of particles which was defined as freeze in granular materials of particles. My aim is to find the torque on this group of particles about its centre when it is placed in the group of particles which was allowed to move.i try fix property/atom but it is giving the torque with respect to the centre of each particle.
The variable command has a torque(group,dim) function which
will give you a component of torque on a group of atoms, based
on forces on the particles around the COM of the group. It will
not include a contribution to torque from the torques on the
individual particles, but that is probably a small effect.
However, if you freeze the group if will zero the forces
on those particles before the variable has a chance to
calculate the torque.
So two other ideas:
a) define the group as a rigid body instead of freezing it,
via the fix rigid command. You can use the force and torque
keywords of fix rigid to prevent it from moving at all,
same as if you’d used freeze. The fix can output
the components of force and torque on the body, and they
will be the components before they are zeroed. Also
they will include the contribution from torques on individual
b) Use the rerun command to post-process a dump file
from your original run. If you don’t use fix freeze in
the rerun input script, then you can use the variable idea
above to get total torque on any group of atoms.