Bond/Angle/Torsion/VdW energies DO NOT change as the uni-axial strain increases

Dear All,

I am doing uni-axial tension on glassy polymers with period boundary conditions along 3 dimensions.

But the Bond/Angle/Torsion/VdW energies DO NOT change as the strain increases, they are just constant during deformations. We use PCFF potential.

As a reference, in “A general inelastic internal state variable model for amorphous glassy polymers” by Bouvard et al, they have the Bond/Angle/Torsion/VdW energies changing as the strain increases. They use DREIDING potential.

Can anyone please help me figure out where this problem from? My input file is below.

Thanks a lot.
Lili Zhang

units real

boundary p p p

atom_style full

pair_style lj/class2 10.0

bond_style class2

angle_style class2

dihedral_style class2

improper_style class2

read_restart restart.ACBPA6030

variable strain equal “ln(1 + (lx - v_L0)/v_L0)”

variable p1 equal “v_strain”

variable p2 equal “-pxx*.101325”

variable p3 equal “-pyy*.101325”

variable p4 equal “-pzz*.101325”

variable p5 equal “pe”

variable p6 equal “7.603e5/vol”

variable p7 equal “(press-pxx-pyy)*.101325”

variable e1 equal “ebond”

variable e2 equal “eangle”

variable e3 equal “edihed”

variable e4 equal “evdwl”

variable tmp equal “lx”

variable L0 equal ${tmp}

print “Initial Length, L0: ${L0}”

timestep 1

fix 1 all nph y 1 1 1000 z 1 1 1000

fix 2 all deform 1 x trate 1e-6 units box remap x

Output strain and stress info to file

for units real, pressure is in [atmospheres]

fix def1 all print 1000 “{p1} {p2} {p3} {p4} {p5} {p6} {e1} {e2} {e3} {e4}” file ACBPA6030.txt screen no

Use cfg for AtomEye

dump 1 all cfg 10000 ACBPA6030_*.cfg id type xs ys zs fx fy fz mol

Display thermo

thermo 100

thermo_style custom step v_strain temp v_p2 v_p3 v_p4 ke pe press v_p6 v_e1 v_e2 v_e3 v_e4 v_p7

run 1000000

It’s not surprising that bond stretching energy does not change, since bonds are pretty stiff and won’t experience stretching until you reach extremely large global strain. But angle and torsion degrees of freedom should be more flexible. The van der Waals energy is actually the major part contributing to the deformation process.

It would be more helpful if you post some plots of energy components (bond, angle, …) versus strain here.


Dear All,

Energy component.jpg

It looks to me that your energies are changing wrt strain. What does it mean when strain is “1”?