The bonds are never breaking

Hello, Dear lammps user,
I wrote a file about polymer (PETG) and then get it in equilibrium and tensile it. But even I run the simulation with long enough time, the bonds will never break(which should be broken actually). Through ovito or vmd I can see that the distance between bond atoms is far enough but the strain stress curve shows that the bonds are not broken.
Here is my in file:
variable project index “PETG” # project name

variable project index “petg” # project name

variable source index …/build # data directory

variable params index …/build # parameter directory

variable temperature index 300 # system temperature

variable tdamp index 100 # temperature damping

variable dielectric index 1 # medium dielectric

variable kappa index 4 # electrostatics kappa

variable cutoff index 9.5 # standard cutoff

variable charge_cutoff index 9.5 # charge cutoff

variable precision index 0.001 # kspace precision

variable lseed index 723853 # langevin seed

variable vseed index 1486234 # velocity init seed

variable tequil index 50000 # equilibration time

variable trun index 10000000 # run time

variable frestart index 0 # 0: equil, 1: restart

variable dtrestart index 100000 # delta restart time

variable dtdump index 100000 # delta dump time

variable dtthermo index 1000 # delta thermo time

variable timestep index 0.5 # integration time step

variable tfreq index 10 # profile sampling freq

variable nsample index 1000 # profile conf sampling

variable dtime equal {tfreq}*{nsample} # profile dtime

variable restart index {params}/{project}.restart

New Variables for output

variable p1 equal “time”

variable p2 equal “vol”

variable p3 equal “pe”

variable p4 equal “temp”

variable p5 equal “etotal”

variable p6 equal “density”

variable p7 equal “mol”

if “${frestart} != 0” then &

“variable data index ${restart}” &

else &

“variable data index ${project}.data” &

LAMMPS atomistic input script

echo screen

units real

atom_style full

Interaction potential definition

pair_style lj/class2/coul/long {cutoff} {charge_cutoff}

bond_style harmonic

special_bonds lj/coul 0 0 1

if “{frestart} != 0" then "read_restart {data}” else “read_data ${data}”

include ${project}.params

Integration conditions (check)

timestep ${timestep}

kspace_style pppm/cg ${precision}

dielectric ${dielectric}

fix mom all momentum 100 linear 1 1 1 angular

Set thermo output

thermo 1000

thermo_style custom step pe etotal temp time vol density

Calculate the mean squared displacement for Multiple chunks of atoms

compute cc1 all chunk/atom molecule

compute msd1 all msd/chunk cc1

#fix msd1 all ave/time 1000 1 1000 c_msd1[*] file tmp.out mode vector

Hello, Dear lammps user,
I wrote a file about polymer (PETG) and then get it in equilibrium and tensile it. But even I run the simulation with long enough time, the bonds will never break(which should be broken actually). Through ovito or vmd I can see that the distance between bond atoms is far enough but the strain stress curve shows that the bonds are not broken.

this is a horribly complex and confusing input, but after some digging, i can find, that you are using bond style harmonic. please look at the shape at that potential and see, that it is impossible to break bonds with that kind of model.

axel.