How to calculate rotational speed of a nanoparticle

Hi
I have a spherical platinium nanoparticle (that includes 100 platinium atoms) in a simulation box that is filled (less than a half) with liquid argon. I want to simulate the boiling process of liquid argon on a copper plain surface. I know that I can log the position and linear velocity of the nanoparticle with below codes:

group         Pt       type       2

variable 	  xcm_x 		equal 		xcm(Pt,x)
variable 	  xcm_y 		equal 		xcm(Pt,y)
variable 	  xcm_z 		equal 		xcm(Pt,z)

variable 	  vcm_x 		equal 		vcm(Pt,x)
variable 	  vcm_y 		equal 		vcm(Pt,y)
variable 	  vcm_z 		equal 		vcm(Pt,z)

fix   Ptloc  Pt ave/time ${Ne} ${Nr} ${Nf} v_xcm_x    v_xcm_y     v_xcm_z     file   Pt_loc.txt
fix   PtVel  Pt ave/time ${Ne} ${Nr} ${Nf} v_vcm_x    v_vcm_y     v_vcm_z    file   Pt_Vel.txt

Now my question is: how can I log the angular velocity of the nanoparticle around x, y and z-axis?

Thanks

Please check out the documentation for the variable command — LAMMPS documentation
There are more functions operating on groups, not just center of mass position and velocity.