Need help: How to model a simulation of nano-machining with LAMMPS

May I ask you a simple questions? (Colored) The version of LAMMPS I used is the latest, I use SVN to update it every day:
My script follows here, It is a simple model, a rigid object moving on a bigger one, scratching or machining. It is a model just to learn.
Thanks, Best Regards.
units metal
boundary p p s
atom_style atomic
neighbor 2.0 bin
neigh_modify delay 5

lattice fcc 4.05
region whole block 0 10 0 20 0 15
create_box 2 whole
create_atoms 2 box

mass 1 1.0
mass 2 1.0

region 1 block 2.5 7.5 16 20 9 INF
region 2 block INF INF INF 14 4 11
region 3 block INF INF INF 14 2 4
region 4 block INF INF INF 14 INF 2

group tool region 1
group newtonian region 2
group thermostat region 3
group boundary region 4

group empty subtract all tool newtonian thermostat boundary

delete_atoms group empty

group mobile union newtonian thermostat boundary

set group tool type 1
set group mobile type 2

pair_style hybrid tersoff morse 2.5 eam
pair_coeff * * tersoff SiC.tersoff C C
pair_coeff 1 2 morse 100.0 2.0 1.5 3.0
pair_coeff 1 1 eam Cu_u6.eam

fix 1 tool rigid single

compute new mobile temp

velocity mobile create 293 5812775 temp new
velocity tool set 0 -20 0

#fix 2 mobile nve

this is far too complex an input to debug it on sight.

you have to build it in parts, check each part of your system
independently, fix all problems that show up and then step by step
combine it. this way you easily see where things go wrong and what


One thing you can’t do is set the velocity of
atoms in a rigid body, via the velocity
command, after the rigid body has been
defined. At that point the rigid body
already has a stored center-of-mass
velocity, and changing the vel of individual
atoms, won’t change it.