Hello,
Please put the lammps mailing list in copy for further questions, so
that the answers can benefit everyone.
You seem to be referring to the "DPD thermostated liquid of LJ chains
sheared between (111) fcc walls " script I posted in the user scripts.
You have to run the perl script (i.e., typing 'perl chain.perl.txt' in
the console) to produce the data file. As mentioned in the
introduction of the input file, for a given liquid viscosity, a
critical parameter controlling the hydrodynamic boundary condition is
the fluid/solid interaction energy (epsilon coefficient of the LJ
potential between fluid and solid atoms). The lower the coefficient,
the lower the interfacial friction, and the larger the slip length.
Typically it's possible to go from no-slip for epsilon_fs ~ epsilon_ff
to a large slip length (tens of sigma) for epsilon_fs ~ 0.2
epsilon_ff. Regarding your question on Couette flow, if you look at
the end of the input script you will see that top and bottom walls are
moved with opposite velocities along the x direction.
Best,
Laurent