Graphene sheet moving in Simulation box

Hello everyone,

I have built 4 layers of graphene sheet which is then stretched uniaxially with CVFF potential in the x-direction with a strain rate of 1e-9/s. The stress-stress curve, Elastic Modulus and poisson ratio are all in the reported range. But the jpg figures and from VMD I can see that the sheets are moving in the simulation box. Shouldn’t they strecth along with the box instead of displacing themselves?I am sending you jpg images to look at it.

Any help will greatly appreciated. Here is part of the input file:

echo screen
log debug_grap.log

units real
atom_style full
boundary p p p

bond_style morse
angle_style harmonic
dihedral_style harmonic
improper_style cvff

pair_style lj/cut/coul/long 10.0 10.0 # cutoff1 = 2.5*sigma

read_data data.grap

kspace_style ewald 1e-4

neighbor 5.0 bin

#neigh_modify delay 0 every 1 one 10000 check yes
neigh_modify delay 0 every 1 check yes

pair_modify mix arithmetic tail no

group graphene type 1

compute tmpall graphene temp
compute mobile_temp graphene temp

variable temp equal “298” # Kelvin
velocity graphene create ${temp} 12345 temp mobile_temp dist uniform mom yes rot no

fix 8 all nvt temp {temp} {temp} 5.0 drag 1
fix 9 all deform 1 x erate ${erate1} units box remap x

fix print all print 100 “{s1} {p1} {p2} {p3} ${p4}” file grap4.defo.txt screen no

timestep 1
thermo 100
#thermo_style custom step temp pe etotal vol press v_strain v_stress lx ly lz
thermo_style custom step temp vol press v_sigmax v_sigmay v_strainx v_mu lx v_gvol
dump 3 all xyz 5000
dump 4 all image 2500 dump.*.jpg type type
run 35000