Uniaxial tensile of graphene

Dear all,

I’m trying to apply uniaxial tensile loading on graphene sheet with the latest Lammps version. The uniaxial deformation is applied via ‘‘velocity’’ command. But the strange problem is that, though the script runs well, there is no axial deformation at all (the box size does not change). I have checked the script many times but could not find out where the bug is. Anyone could help me about this? My script is as follows:

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dimension 3
boundary p s s
units metal
atom_style atomic

neighbor 2.0 nsq
neigh_modify every 10 check yes

read_data graphene.dat

potentials

pair_style airebo 2.0
pair_coeff * * CH.airebo C
mass 1 12.0

groups

region Ledge block INF 6.0 INF INF INF INF units box
region Redge block 332.0 INF INF INF INF INF units box

group left region Ledge
group right region Redge
group boundary union left right
group mobile subtract all boundary

initial velocities

velocity all create 300.0 5201314 dist gaussian
velocity all zero linear
velocity all zero angular

compute myTemp mobile temp

thermo 500
thermo_style custom step c_myTemp etotal lx ly lz pxx pyy pzz

dump 1 all atom 500 equil.lammpstrj

energy equilibration

min_style cg
minimize 1.0e-15 1.0e-10 10000 10000

velocity boundary set 0.0 0.0 0.0

fix 1 boundary setforce NULL NULL 0.0
fix 3 mobile nvt temp 300.0 300.0 0.1
fix_modify 3 temp myTemp

reset_timestep 0
run 10000

unfix 3
unfix 1
undump 1

tensile deformation

reset_timestep 0

fix 1 boundary setforce 0.0 0.0 0.0
fix 3 mobile nvt temp 300.0 300.0 0.1
fix_modify 3 temp myTemp

velocity left set -0.17 0.0 0.0
velocity right set 0.17 0.0 0.0

thermo_style custom step c_myTemp etotal lx ly lz pxx pyy pzz
dump 1 all atom 1000 deform.lammpstrj

variable stress equal -pxx0.1 #MPa
variable strain equal step
0.000001 #

fix def_print all print 1000 “{strain} {stress}” file curve.dat screen no

run 300000
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Thank you so much!

Best regards,

WL

graphene.dat (479 KB)

If you are not integrating your boundary atoms they
won’t move, no matter what their velocity or

forces on them.

Steve