# force dumping from rigid body problem

Dear Steve,

We define part of system as a rigid body and give a constant velocity to it. Then we dump the sum of the forces on the rigid body during the simulation. Instead of giving an average steady state 0 value, it gives a constant value. That doesn’t make sense, since the whole system is moving together with the velocity given to the rigid body

Please see the below script we used:

units metal

# time:ps; distance: Angstrom; energy: eV; force:eV/A=1.6 nN;

atom_style hybrid atomic

boundary p p p

timestep 0.001

group bot type = 1

group therm1 type = 2

group film type = 3

group tipdown type = 4

group therm2 type = 5

group tiptop type = 6

group tip union tipdown therm2 tiptop

group sub union bot therm1 film

group mobile subtract all bot

group subnve subtract all tiptop

group tem union therm2 therm1

group dump union tip film

pair_style hybrid/overlay tersoff table linear 1000

pair_coeff * * tersoff SiC.tersoff C C C C C C

pair_coeff 3 4*5 table lj.table CC 10.0

fix 1 bot setforce 0 0 0

velocity mobile create 300.0 23456789 units box

fix 2 mobile langevin 300.0 300.0 0.01 699483

compute 1 tiptop reduce sum fx

compute 2 tiptop reduce sum fz

compute new3d mobile temp

fix 13 tiptop ave/time 1 7350 7350 c_1 file tiptop-fx1

fix 14 tiptop ave/time 1 7350 7350 c_2 file tiptop-fz1

dump 1 dump cfg 7350 dump.*.cfg id type xs ys zs x y z id type

thermo_style custom step temp etotal press vol lx ly lz

thermo 7350

thermo_modify temp new3d

# Cutting speed: 1.0 A/ps = 100 m/s

#fix 3 tiptop nve/noforce

#fix 4 subnve nve

#unfix 3

#unfix 4

fix 21 tiptop rigid/nve single force * on on on torque * off off off

fix 22 subnve nve

velocity tiptop set 0.2 0 0 units box

run 1000000

Thanks

Zhendong