undesirable movement of the simulation box in NVT ensemble

Dear lammps users

I am going to perform a scratch on the surface of an epoxy. However, while I am running the equilibrated system in the NVT ensemble, the box moves up constantly. All parameters including energy, temperature, and volume are in the steady condition. Can anyone explain why the box moves up? Can anyone give me a suggestion to fix the problem.

Thank you very much for your helps in advance
bests,

Saeed Doagou-R
[email protected]…24…

An example of my code can bee seen below:

3D Pure Epoxy Simulation

boundary p p s
units metal

#neighbor 1 bin
neigh_modify delay 5

atom_style full

read_data data90.txt

special_bonds amber

defenition of forcefield

pair_style lj/charmm/coul/charmm 6 8

pair_coeff 1 1 0.0047042 3.399669508
pair_coeff 1 2 0.004170867 3.399669508
pair_coeff 1 3 0.005864103 3.324834016
pair_coeff 1 4 0.005864103 3.199840926
pair_coeff 1 5 0.00652379 3.233071448
pair_coeff 1 6 0.001782079 2.234373985
pair_coeff 1 7 0.0000 1.699834754
pair_coeff 1 8 0.001741898 2.999655984
pair_coeff 1 9 0.001782079 3.024601148
pair_coeff 2 2 0.003698 3.399669508
pair_coeff 2 3 0.005199267 3.324834016
pair_coeff 2 4 0.005199267 3.199840926
pair_coeff 2 5 0.005784163 3.233071448
pair_coeff 2 6 0.001580038 2.234373985
pair_coeff 2 7 0 1.699834754
pair_coeff 2 8 0.001544413 2.999655984
pair_coeff 2 9 0.001580038 3.024601148
pair_coeff 3 3 0.00731 3.249998524
pair_coeff 3 4 0.00731 3.125005434
pair_coeff 3 5 0.008132345 3.158235956
pair_coeff 3 6 0.002221482 2.159538493
pair_coeff 3 7 0 1.624999262
pair_coeff 3 8 0.002171394 2.924820492
pair_coeff 3 9 0.002221482 2.949765656
pair_coeff 4 4 0.00731 3.000012343
pair_coeff 4 5 0.008132345 3.033242866
pair_coeff 4 6 0.002221482 2.034545403
pair_coeff 4 7 0 1.500006172
pair_coeff 4 8 0.002171394 2.799827401
pair_coeff 4 9 0.002221482 2.824772566
pair_coeff 5 5 0.0090472 3.066473388
pair_coeff 5 6 0.002471389 2.067775925
pair_coeff 5 7 0 1.533236694
pair_coeff 5 8 0.002415666 2.833057924
pair_coeff 5 9 0.002471389 2.858003088
pair_coeff 6 6 0.0006751 1.069078462
pair_coeff 6 7 0 0.534539231
pair_coeff 6 8 0.000659878 1.834360461
pair_coeff 6 9 0.0006751 1.859305625
pair_coeff 7 7 0 0
pair_coeff 7 8 0 1.29982123
pair_coeff 7 9 0 1.324766394
pair_coeff 8 8 0.000645 2.59964246
pair_coeff 8 9 0.000659878 2.624587624
pair_coeff 9 9 0.0006751 2.649532788

bond_style harmonic

bond_coeff 1 13.33 1.526
bond_coeff 2 13.76 1.41
bond_coeff 3 12.9 1.4
bond_coeff 4 20.167 1.4
bond_coeff 5 13.631 1.51
bond_coeff 6 14.491 1.449
bond_coeff 7 18.662 1.01
bond_coeff 8 13.76 1.41
bond_coeff 9 14.62 1.09
bond_coeff 10 15.781 1.08
bond_coeff 11 23.779 0.96

angle_style charmm

angle_coeff 1 1.505 109.5 0 0
angle_coeff 2 2.15 109.5 0 0
angle_coeff 3 1.72 109.5 0 0
angle_coeff 4 2.15 109.5 0 0
angle_coeff 5 2.15 109.5 0 0
angle_coeff 6 2.365 108.5 0 0
angle_coeff 7 2.58 109.5 0 0
angle_coeff 8 2.15 118.4 0 0
angle_coeff 9 1.505 120 0 0
angle_coeff 10 3.01 120 0 0
angle_coeff 11 2.709 120 0 0
angle_coeff 12 3.01 120 0 0
angle_coeff 13 2.709 114 0 0
angle_coeff 14 3.01 109.5 0 0
angle_coeff 15 3.44 109.7 0 0
angle_coeff 16 2.15 118 0 0
angle_coeff 17 2.66 113 0 0
angle_coeff 18 2.1887 108.7 0 0
angle_coeff 19 2.15 109.5 0 0
angle_coeff 20 1.505 109.5 0 0

dihedral_style charmm

dihedral_coeff 1 0.049 3 0 0
dihedral_coeff 2 0.0602 3 0 0
dihedral_coeff 3 0.0602 3 0 0
dihedral_coeff 4 0.049 3 0 0
dihedral_coeff 5 0.0602 3 0 0
dihedral_coeff 6 0.0602 3 0 0
dihedral_coeff 7 0.0602 3 0 0
dihedral_coeff 8 0.049 3 0 0
dihedral_coeff 9 0.049 3 0 0
dihedral_coeff 10 0.15 2 180 0
dihedral_coeff 11 0.6235 2 180 0
dihedral_coeff 12 0.6235 2 180 0
dihedral_coeff 13 0.6235 2 180 0
dihedral_coeff 14 0.6235 2 180 0
dihedral_coeff 15 0.6235 2 180 0
dihedral_coeff 16 0 2 0 0
dihedral_coeff 17 0.6235 2 180 0
dihedral_coeff 18 0.0602 3 0 0
dihedral_coeff 19 0 2 0 0
dihedral_coeff 20 0.6235 2 180 0
dihedral_coeff 21 0.0215 3 0 0
dihedral_coeff 22 0.0215 3 0 0
dihedral_coeff 23 0.0602 3 0 0
dihedral_coeff 24 0.0602 3 0 0
dihedral_coeff 25 0 2 0 0
dihedral_coeff 26 0.0602 3 0 0
dihedral_coeff 27 0.0602 3 0 0
dihedral_coeff 28 0.0602 3 0 0
dihedral_coeff 29 0 2 0 0
dihedral_coeff 30 0 2 0 0
dihedral_coeff 31 0 2 0 0
dihedral_coeff 32 0.0602 3 0 0

velocity all create 300 2349852
fix wall all wall/lj126 zlo -46.0 0.01 2 10.0 units box

I don’t know what “the box moves up” means
or how you are monitoring it. You have a zlo
wall. If you are pushing atoms against it

(to make a scratch?), then they may reflect
upward.

Steve