Dear lammps-users,
I was hoping someone might be able to point me in the right direction for a problem I have...
I am trying to model nano cutting of copper with a diamond indenter. At the moment, the copper atoms explode outwards when the simulation begins. I am using a copper setup used by most - a fixed outer layer (bottom and left), just inside this a fixed 300K thermo layer, then the moveable copper atoms.
The temperature and pressure may be the reason as they are fluctuating quite a bit, but I don't understand why...
Can anyone see a reason why this might be occurring?
Below is the input script:
units metal
dimension 3
boundary s s s
# Create Simulation Box
lattice fcc 3.3 orient y 1 -1 0 orient x 1 1 1 orient z 1 1 -2
region box block 0 30 0 15 0 16
create_box 2 box
# Create bench
region cop block 0 16 0 8 0 16
lattice fcc 3.3 orient x 1 1 1 orient y 1 -1 0 orient z 1 1 -2
create_atoms 1 region cop
# Create indenter
lattice none
lattice diamond 3.3 orient x 1 1 1 orient y 1 -1 0 orient z 1 1 -2
region cyl cylinder z 20 10 2 7 9 # (x=20,y=10,r=2,zlo=7,zhi=9)
region front block 18 18.5 10 14 7 9
region back prism 20.414 21.414 8.586 15 7 9 10 0 0
region pin union 3 cyl front back
create_atoms 2 region pin
region bott block INF INF INF 1 INF INF
region left block INF 1 INF INF INF INF
region b block 1 16 1 2 INF INF
region l block 1 2 1 8 INF INF
group bott region bott # bottom layer
group left region left # left layer
group b region b
group l region l
group cu region cop
group pin region pin # indenter
group mob subtract cu bott left # moveable copper atoms
group exc union left bott pin # atoms that won't move
group therm union b l # thermo atoms
mass 1 63.546
mass 2 12.011
pair_style hybrid morse 4.5 eam
pair_coeff * * eam /Users/tim/Lammps/lammps-6Dec08/potentials/Cu_u3.eam
pair_coeff 1 2 morse 4.5 0.087 5.14 2.05
neighbor 2.0 bin
neigh_modify delay 5 exclude group exc exc
dump 1 all xyz 1000 dump.sim8
fix 12 therm temp/rescale 1.0 300 300 0.1 1.0
fix 5 pin nve/noforce
fix 10 mob nve
timestep 0.005
thermo 10
thermo_modify lost warn
thermo_style custom step temp press etotal pe
run 2000
velocity pin set -1 0 0 sum yes units box # give the indenter velocity 1A/ps in the x direction
run 8000
I have been through the manual trying to understand what could be happening, but have so far been unable to find it out.. If possible, thankyou for any advice.
Tim