Problem with "fix rigid"

Dear lammps users,

Now I’m trying to simulate the movement of a carbon nanotube in fluid. I want to treat the CNT as a rigid body using the “fix rigid” command. Also, I want the velocity of the carbon atoms vz (velocity along z direction) to be zero. This means the CNT will only translate and rotate on the x-y plane.

My code is like:

fix 1 cnt rigid single force * on on off torque * on on off

But vz is still not zero.

Also, I find “fix setforce” cannot be used along with “fix rigid”. Actually, if I delete the “fix rigid” command and use “velocity set” and “fix setforce”, vz of the carbon atoms can be set to zero.

I’m looking forward to having your help.

Best wishes
Ruo-Yu Dong

Hi Ruo-dong,

in addition to setting velocity vz being 0.0, you may want to change the torque flag to be “off off on” to keep the CNT rotate in the x-y plane only.