Class2 and carbon nanotube

Hello everyone.
I am LAMMPS beginner and try strain simulation in carbon nanotube.

I am aiming to compress the carbon nanotube in the axis direction and obtain the Young’s modulus.

I did this simulation on airebo, and got good result.

However, I did the same simulation on class2 and I could not get good results.

Specifically, it shows much higher pressure than the airebo result.

The input file is shown below, strain simulation was done after relaxation simulation.

The data file was created using the nanotube builder of VMD and added bond (and angle, so on) for periodic boundary.

Please tell me how to solve this probrem.

----------------relaxation---------------
units metal

boundary f f p

atom_style full

pair_style lj/class2 3

bond_style class2

angle_style class2

dihedral_style class2

improper_style class2

mass 1 12.0

pair_coeff * * 0.068 3.915

bond_coeff * 1.4170 470.8361 -627.6179 1327.6345

angle_coeff * 118.9000 61.0226 -34.9931 0.0000

angle_coeff * bb 68.2856 1.4170 1.4170

angle_coeff * ba 28.8708 28.8708 1.4170 1.4170

dihedral_coeff * 8.3667 0.0000 1.2000 0.0000 0.0000 0.0000

dihedral_coeff * mbt 27.5989 -2.3120 0.0000 1.4170

dihedral_coeff * ebt -0.1185 6.3204 0.0000 -0.1185 6.3204 0.0000 1.4170 1.4170

dihedral_coeff * at 1.9767 1.0239 0.0000 1.9767 1.0239 0.0000 118.9000 118.9000

dihedral_coeff * aat 0.0000 118.9000 118.9000

dihedral_coeff * bb13 53 1.4170 1.4170

improper_coeff * 7.1794 0.0000

improper_coeff * aa 0.0000 0.0000 0.0000 118.9000 118.9000 118.9000

velocity all create 1.0 780042

fix 1 all nve

fix 2 all temp/rescale 1 1.0 1.0 0.05 1.0

fix 3 all press/berendsen z 0.0 0.0 500.0

----------------stress---------------

units metal

boundary f f p

atom_style full

pair_style lj/class2 3

bond_style class2

angle_style class2

dihedral_style class2

improper_style class2

fix 1 all nve

fix 2 all temp/rescale 1 1.0 1.0 0.05 1.0

fix 3 all deform 1 z trate -0.001

There is no expectation that different force field models
should yield identical or even similar answers. Different
force fields are fit to different properties.

Steve