Particle Interactions

I'm trying to calibrate rotational particle interaction values. In setting up the problem I noticed with the absence of applied forces, gravity and, damping that my particles were moving. Upon investigation I found that the particle interaction values are causing the particles to move. As I adjust the interaction values the particles move in different manners. How is this possible? Since no forces are being applied the particles should never move. My code is shown below.

I realize the interaction values in the code are not reasonable but, the values should not cause the particles to move in the absence of forces.

Thanks.

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from esys.lsm import *
from esys.lsm.util import *
from esys.lsm.geometry import *
from POVsnaps import POVsnaps

sim = LsmMpi(numWorkerProcesses=8, mpiDimList=[4,2,1])
sim.initNeighbourSearch(
   particleType="RotSphere",
   gridSpacing=.625,
   verletDist=0.05
)

sim.setNumTimeSteps(100)
sim.setTimeStepSize(1)

domain = BoundingBox(Vec3(-20,-20,-20), Vec3(20,20,20))
sim.setSpatialDomain(domain)

r = .25 #radius

cube = CubicBoxPacker (
   radius = r,
   bBox = BoundingBox(
      Vec3(-0.50,1.75,-0.00),
      Vec3(4.50,2.25,0.00)
   ),
   circDimList = [False, False, False],
   tolerance = 1.0000e-05
)
cube.generate()
cube_particles = cube.getSimpleSphereCollection()

sim.createParticles(cube_particles)

sim.createConnections(
   ConnectionFinder(
      maxDist = 0.5,
      bondTag = 0,
      pList = cube_particles
   )
)

pp_bonds = sim.createInteractionGroup (
   RotBondPrms(
      name="pp_bonds",
      normalK=0.0005,
      shearK=0.0005,
      torsionK=0.0005,
      bendingK=0.0005,
      normalBrkForce=1000,
      shearBrkForce=1000,
      torsionBrkForce=1000,
      bendingBrkForce=1000,
      tag=0,
      scaling = True
   )
)

povcami = POVsnaps(sim=sim, interval=1)
povcami.configure(lookAt=Vec3(2,2,0), camPosn=(2,2,5), zoomFactor=0.2)
sim.addPostTimeStepRunnable(povcami)

sim.run()