Graphene stress-strain curve

Dear all,

I am simulating graphene 50*11 Ang. under tensile using airebo force field.

After simulation stress-strain curve give an ultimate strain in 0.4 at 210 Gpa stress. It is more strange rather than what others found before.

I found the Ultimate strain from 0.12 to 0.22 in other references.

my input file is as follow: (Could you please help me in this issue?)

------------------------ INITIALIZATION ----------------------------

units metal
dimension 3
boundary p p p
atom_style atomic
newton on

----------------------- ATOM DEFINITION ----------------------------

read_data data.grap.txt

mass 1 12.000

------------------------ FORCE FIELDS ------------------------------

pair_style airebo 3.0
pair_coeff * * CH.airebo C

------------------------- SETTINGS ---------------------------------

#-------------system equilibrium before deformation-------------------
reset_timestep 0
timestep 0.001
fix 1 all npt temp 300 300 2 iso 0 0 1 drag 1
thermo 1000

thermo_style custom step lx ly pxx pyy press pe temp

##-------------Running relaxation------------------
run 20000

unfix 1

#---- Final length at z direction----

Store final cell length for strain calculations

variable tmp equal “ly”
variable L0 equal {tmp} print "Initial Length, L0: {L0}"

Check your reference point (0 strain, 0 stress) when plotting your Stress-Strain Curve.

Dear Xiaolin,

My reference point does not have any problem. I heard that after each iteration or dynamic run I should allow the system to be relaxed!

But I do not know how I have to do this deal.

I will appreciate everybody help me in this issue.

B. regards

Amir