Harmonic conflicts with coulomb potential

Hi, I am new to LAMMPS, I am writing a simple script with harmonic and coulomb potentials. The problem I had is that the coulomb potential is not contributing at all. I output the system energy which contains only harmonic potential(I ran simulation with harmonic only and coulomb only, the energy matches with harmonic. while I am expecting the sum). I wonder where I did wrong. Thanks for the help.

my script is:

units si
atom_style full
boundary p p p
read_data tet_sc.data
bond_style harmonic
bond_coeff 1 0.5 1.3
pair_style coul/cut 15.0
pair_coeff * * 
velocity all set 0.0 0.0 0.0
fix 1 all nve
variable myPE equal pe
variable myKE equal ke
timestep 0.02
dump mydump all xyz 1 dump.xyz
run 100

and my tet_sc.data is:

LAMMPS data file.
4 atoms
6 bonds

1 atom types
1 bond types

-15.0 15.0 xlo xhi
-15.0 15.0 ylo yhi
-15.0 15.0 zlo zhi

Masses

1 1.0

Atoms

1 1 1 8e-6 0.0 0.0 0.0
2 1 1 8e-6 1.0 0.0 0.0
3 1 1 8e-6 0.0 1.0 0.0
4 1 1 8e-6 0.0 0.0 1.0

Bonds

1 1 1 2
2 1 1 3
3 1 1 4
4 1 2 3
5 1 2 4
6 1 3 4

Besides the physics of your system, the special_bonds command set by default to zero all pairwise interactions for bonded atoms. Like in your input system.

2 Likes

thank you! That is my lifesaver!