lammps/examples/friction/in.friction

# 2d friction simulation

dimension	2
boundary	p s p

atom_style	atomic
neighbor	0.3 bin
neigh_modify	delay 5

# create geometry

lattice		hex 0.9
region		box block 0 50 0 22 -0.25 0.25
create_box	4 box

mass		1 1.0
mass		2 1.0
mass		3 1.0
mass		4 1.0

# atom regions

region          lo-fixed block INF INF INF 1.1 INF INF
region          lo-slab block INF INF INF 7 INF INF
region          above-lo block INF INF INF 7 INF INF side out
region          hi-fixed block INF INF 20.9 INF INF INF
region          hi-slab block INF INF 15 INF INF INF
region          below-hi block INF INF 15 INF INF INF side out
region		lo-asperity sphere 32 7 0 8
region		hi-asperity sphere 18 15 0 8
region		lo-half-sphere intersect 2 lo-asperity above-lo
region		hi-half-sphere intersect 2 hi-asperity below-hi

# create 2 surfaces with asperities

create_atoms	1 region lo-slab
create_atoms	1 region hi-slab
create_atoms	2 region lo-half-sphere
create_atoms	3 region hi-half-sphere

# LJ potentials

pair_style	lj/cut 2.5
pair_coeff	* * 1.0 1.0 2.5

# define groups

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

# initial velocities

compute         new mobile temp/partial 0 1 0
velocity	mobile create 0.1 482748 temp new
velocity	hi set 1.0 0.0 0.0 sum yes

# fixes

fix		1 all nve
fix		2 boundary setforce 0.0 0.0 0.0
fix		3 mobile temp/rescale 200 0.1 0.1 0.02 1.0
fix_modify	3 temp new
fix             4 all enforce2d

# Run

timestep	0.0025
thermo		1000
thermo_modify	temp new

#dump		1 all atom 500 dump.friction

#dump		1 all image 500 image.*.jpg type type &
#		zoom 1.6 adiam 1.5
#dump_modify	1 pad 5

run		20000