Dear all,
I am doing friction simulation setting the velocity of 0.5 (angstoms/picosecond) in x direction to simulate velocity of 50m/s.
However, the result showed atoms mixed up with increase of volume and decrease of pressure.
After I increase the velocity to 500, I could get a good result of friction simulation.
This is confusing because 500 in metal unit means 50000m/s.
I have triedâ€¦

Very low timestep (0.00001, 0.000001)

Nvt instead of nve and temp/rescale

lower neighbor 2.0

lower cutoff of airebo (2.0, 1.0)
None of them worked.
Can anybody give me a hint to drive a good result of simulation with velocity of 0.5 (50m/s) in this simulation?
Below is modified in.friction example file which is from lammps package. (red colored are critical changes)
Thank you,
Sungae Lee
2d friction simulation
dimension 2
boundary p s p
units metal
atom_style full
neighbor 10 bin
neigh_modify delay 5
create geometry
lattice hex 3
region box block 0 50 0 30 0.25 0.25 units box
create_box 4 box
mass 1 12.01
mass 2 12.01
mass 3 12.01
mass 4 12.01
atom regions
region lofixed block INF INF INF 2 INF INF units box
region loslab block INF INF INF 10 INF INF units box
region abovelo block INF INF INF 10 INF INF side out units box
region hifixed block INF INF 25 INF INF INF units box
region hislab block INF INF 17 INF INF INF units box
region belowhi block INF INF 17 INF INF INF side out units box
region loasperity sphere 32 10 0 5 units box
region hiasperity sphere 18 17 0 5 units box
region lohalfsphere intersect 2 loasperity abovelo units box
region hihalfsphere intersect 2 hiasperity belowhi units box
region outboxes intersect 2 abovelo belowhi units box
region asperities union 2 lohalfsphere hihalfsphere units box
create 2 surfaces with asperities
create_atoms 1 region loslab
create_atoms 2 region hislab
create_atoms 3 region lohalfsphere
create_atoms 4 region hihalfsphere
LJ potentials
pair_style airebo 3.0 0 0
pair_coeff * * CH.airebo C C C C
define groups
group lo region loslab
group lo type 1 3
group hi region hislab
group hi type 2 4
group lofixed region lofixed
group hifixed region hifixed
group boundary union lofixed hifixed
group mobile subtract all boundary
group outboxes region outboxes
group asperities region asperities
group air subtract outboxes asperities
group noair subtract all air
#set group lofixed type 4
#set group hifixed type 4
initial velocities
compute new mobile temp/partial 0 1 0
velocity mobile create 300 482748 temp new units box
velocity hi set 0.5 0.0 0.0 sum yes units box
fixes
fix 1 all nve
fix 2 boundary setforce 0.0 0.0 0.0
fix 3 mobile temp/rescale 10 300 300 10 1 units box
fix_modify 3 temp new