Dear LAMMPS users,
I am deforming granular assemblies in June17 '13 LAMMPS, and I hoped for some clarification about the temp/sphere compute. I have copied my input script at the bottom of the message.
In the compute temp code, the temp is given by:
\sum (m v^2)
In compute temp/sphere, the temp is given by:
\sum (m v^2 + 0.4mr^2 * omega^2)
if we include all degrees of freedom, or:
\sum (0.4mr^2 * omega^2)
if we only include rotational degrees of freedom.
I would expect, therefore, that if we sum the output from the following 2 computes:

compute 1 all temp

compute 2 all temp/sphere dof rotate
we should recover the temperature calculated from this compute:
 compute 3 all temp/sphere dof all
Instead I find that compute 3) is giving the mean of 1) and 2) rather than the total.
Postprocessing the particle velocities independently, I am able to match compute 1) from the translational particle data and compute 2) from the rotational particle data, but when I add these contributions, the result is 2x the output from compute 3) (i.e. it is the sum of 1) and 2) rather than the mean).
Have I misunderstood how we should be adding the translational+rotational contributions in this case?
Many thanks,
Chris
read_restart restart.restart (atom_style = sphere, boundary = p p p, region prism)
newton off
communicate single vel yes
neighbor 0.2 bin
neigh_modify delay 0
pair_style gran/hooke/history 20000 NULL 10 NULL 0.5 1
pair_coeff * *
timestep 0.000114
velocity all zero linear
velocity all zero angular
fix 1 all nve/sphere
compute 1 all temp
compute 2 all temp/sphere dof rotate
compute 3 all temp/sphere dof all
compute 4 all temp/deform
#compute 4 all pressure 3
compute 6 all coord/atom 1.0
variable T_tot equal c_1+c_2
thermo_style custom step c_1 c_2 v_T_tot c_3 c_4
thermo 50000
thermo_modify lost ignore norm no
compute_modify thermo_temp dynamic yes
fix 2 all deform 1 xy erate 10 remap v
dump id all custom 100 a1.dump id vx vy vz omegax omegay omegaz
thermo 100
run 50000