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Hello, my name is Nikitin Egor, I am a student of the Rostov University of railway transport. At the moment I’m writing my thesis in which I use Lammps software product. I need to reproduce the simulation of friction between two surfaces between which the lubricant is present. Now I built two surfaces, but to place between the grease I have is the difficulty. Tell me how can I solve my problem? Code is attached below.

units metal
boundary p p s

atom_style atomic
lattice bcc 2.855324
region box block 0 30.0 0 16.0 0 20.0
create_box 4 box

pair_style eam/fs
pair_coeff * * Fe_mm.eam.fs Fe Fe Fe Fe

neighbor 0.3 bin
neigh_modify delay 5

region lo-fixed block INF INF INF INF INF 1.8
region lo-slab block INF INF INF INF INF 5.0
region above-lo block INF INF INF INF INF 5.0 side out
region hi-fixed block INF INF INF INF 18.2 INF
region hi-slab block INF INF INF INF 15.0 INF
region below-hi block INF INF INF INF 15.0 INF side out

create_atoms 1 region lo-slab
create_atoms 1 region hi-slab

group lo region lo-slab
group lo type 2
group hi region hi-slab
group hi type 3
group lo-fixed region lo-fixed
group hi-fixed region hi-fixed
group boundary union lo-fixed hi-fixed
group mobile subtract all boundary

set group lo-fixed type 4
set group hi-fixed type 4

temp controllers

compute new3d mobile temp
compute new2d mobile temp/partial 0 1 1


velocity mobile create 300.0 5812775 temp new3d
fix 1 all nve
fix 2 boundary setforce 0.0 0.0 0.0

fix 3 mobile temp/rescale 10 300.0 300.0 10.0 1.0
fix_modify 3 temp new3d

thermo 200
thermo_modify temp new3d

timestep 0.001
run 2000


velocity hi-fixed set 0.05 0.0 0.0 sum yes

unfix 3

fix 3 mobile temp/rescale 10 450.0 450.0 10.0 1.0
fix_modify 3 temp new2d

dump 1 all atom 2000 dump.fe_nve
thermo 2000
thermo_modify temp new2d

#reset_timestep 0
#run 4000

If you need to insert atoms or small molecules in a confined
space, you are probably better off using PackMol or
some other pre-processor that is designed to build
complex geometries. See the LAMMPS webpage on
PrePost tools.