Problem with "fix addtorque"

Dear lammps users.

Now I’m trying to simulate the movement of a carbon nanotube in fluid. I treat the CNT as a rigid body using the “fix rigid” command.
Also, the CNT can only rotate around on the x-y plane. The codes are as follows:

velocity cnt set 0.0 0.0 0.0 units box
fix 1 cnt rigid single force * off off off torque * off off on

The above works perfectly. Now, I want to add external torque on the nanotube. Then, the following code is used:

fix 3 cnt addtorque v_tx v_ty 0

Unfortunately, it doesn’t seem to work. Where is the problem?

I’m looking forward to having your help.

Best wishes
Ruo-Yu Dong

Have you installed USER MISC Package ?