[lammps-users] Question about setting group of atoms as rigid body

Dear All

Currently, I want to fix a group of atoms, let's say group A, as a rigid body and give these atoms a constant velocity. So instead of using 'fix rigid', i set the force and velocity of atoms in group A to be zero ( using 'fix setforce' and 'velocity set', and by dong this I can get the force acting on this group before constraint) . By doing this, I guess the atoms in group A should not have any relative movement corresponding to each other , but the simulation does give some position changing for these atoms beside the desired rigid body movement. I am not sure whether what I do here is correct for my purpose.
Thanks for any suggestion in addvance!

Best
Yi

If you set the initial velocity to 0 and the force to
0 and don't otherwise thermostat those atoms, then
they shouldn't move at all during a simulation. If they
are, then you must be using them in some other command,
like a thermostat and integrator fix.

Steve