After some playing around with the input file and reading the LAMMPS
manual, I think I know why you see no shear forces on lower region
inspite of upper region sliding. My arguments are as follows ->
You define a region "boundary" which is the union of your "upper"
region and "lower" region (in fact this encompasses your full
simulation box). Then you use "fix 2 boundary setforce 0.0
0.0 0.0" which fixes all the atoms in region "boundary" thereby
setting the forces on all your atoms to 0.0 along X, Y and Z. Then you
give a velocity to "upper" region, which moves. The lower regions are
not re-fixed and therefore does not move because no forces on them
I would recommend that you try a fix nve on the lower region. You
should also probably create a "real boundary" region as in the "shear"
example wherein the boundary atoms are fixed.
2008/8/12 dinesh kumar <[email protected]>: