units           lj
lattice         fcc 0.8442
boundary        f f f

region          ball   sphere   0.0 0.0 0.0 5.0
region          box    block  -10 10 -10 10 -10 10
region          half   block  -10  0 -10 10 -10 10

# add molecule ids so we can use chunk/atom
fix             0   all property/atom mol ghost yes

create_box      2  box
create_atoms    1  region ball

pair_style      lj/cut 4.0
pair_coeff      * *  1.0 1.0
mass            *    1.0
set             group all mol 1

# label half the sphere with a different type for better visualization
set             region half   type 2

# use a dynamic group (may require a patch to fix addtorque with older versions of LAMMPS)
group           ball   dynamic all   region ball

neigh_modify    delay 2  every 1  check yes

minimize        0.0  0.0    1000  10000
reset_timestep  0

velocity        all create 1.2 12351235

fix             1   all  nve
fix             2   all  wall/reflect  xlo EDGE xhi EDGE ylo EDGE yhi EDGE zlo EDGE zhi EDGE

compute 1 all chunk/atom molecule
compute 2 ball omega/chunk 1
compute 3 ball inertia/chunk 1

# compute rotational kinetic energy: 1/2 * I * omega**2
variable r_ke_x equal c_2[1][1]*c_2[1][1]*c_3[1][1]*0.5
variable r_ke_y equal c_2[1][2]*c_2[1][2]*c_3[1][2]*0.5
variable r_ke_z equal c_2[1][3]*c_2[1][3]*c_3[1][3]*0.5

# output moments of inertia for x,y,z and angular velocity as well as rotational kinertic energy

thermo_style custom step ke pe c_3[1][1] c_3[1][2] c_3[1][3] c_2[1][1] c_2[1][2] c_2[1][3] v_r_ke_x v_r_ke_y v_r_ke_z
thermo 500

# dump 1 all atom 100 dump.lammpstrj

# dump 2 all movie 10 ball.mp4 type mass

# equilibration w/o torque added
run 1000 post no

# start spinning the ball. rotation around z should increase and Erot_z should grow
fix 4 ball addtorque 0.0 0.0 200.0
run 10000 upto  post no

# continue without adding more torque. rotation continues at fixed speed
unfix 4
run 5000