Dear Steve,

Thanks for your response. I figured that out in the weekend I forgot to take down the question.

But now I have another problem, which I really appreciate if you can help me figure that out. I’m modeling a lubricant on top of an Al block, and I’m applying two forces:

1- velocity applied to the block

2- gravity

I observed two behavior which are not correct, so I was wondering if you can help me out understand those:

1- When I apply velocity to the lower layers of the block, just that region moves and the rest of the block is not moving. The only thing that I can think of is the velocity that I apply causes much higher forces than available lj potential forces which overcome the lj force, so I’m trying to lower the velocity but so far, I didnt see any change.

2- The gravity force also makes the Al block gets more packed, I think it causes by the same reason, high forces.

Sorry this questions are not directly related to the LAMMPS but since I’m a newbie in LAMMPS I would really appreciate your help.

Here is my code by far:

# ------------------------------- Initialization Section --------------------

units real

atom_style full

bond_style hybrid harmonic

angle_style hybrid harmonic

dihedral_style hybrid fourier

improper_style hybrid cvff

pair_style hybrid eam/alloy lj/cut 10.0

# ------------------------------- Atom Definition Section -------------------

read_data system.data

# ------------------------------- Settings Section --------------------------

pair_coeff * * eam/alloy Al99.eam.alloy Al Al NULL

pair_coeff 3 3 lj/cut 0.0150 2.59964245953

pair_coeff 2 2 lj/cut 0.0860 3.39966950842

pair_coeff 1 3 lj/cut 0.0150 2.59964245953

pair_coeff 1 2 lj/cut 0.0860 3.39966950842

bond_coeff 1 harmonic 478.4 1.3870

bond_coeff 2 harmonic 344.3 1.0870

angle_coeff 1 harmonic 67.18 119.97

angle_coeff 2 harmonic 48.46 120.01

dihedral_coeff 1 fourier 1 3.625 2 180.0

improper_coeff 1 cvff 1.1 -1 2

region lo-fixed block INF INF INF INF INF 8.1

region lo-slab block INF INF INF INF INF 24.3

region above-lo block INF INF INF INF INF 24.3 side out

region hi-fixed block INF INF INF INF 46.2 INF

region hi-slab block INF INF INF INF 30 INF

region below-hi block INF INF INF INF 30 INF side out

group lo-slab region lo-slab

group above-lo region above-lo

group hi region hi-slab

group lo-fixed region lo-fixed

group hi-fixed region hi-fixed

group boundary union lo-fixed hi-fixed

group mobile subtract all boundary

# ------------------------------- Run Section -------------------------------