Hi, I am having some issues using the bond_style zero available in LAMMPS (23 Mar 2016). It is my understanding that by adding bonds to the system and assigning the bond_style “zero”, there should be no additional energy contributions to the system and the bonds are there just for tracking purposes. However, I discovered noticeable deviations in the energy of my system so I made a decided to make a small sample to double check.

In my sample model, I have created a two layer system of copper atoms and have assigned the top half to type 1 and bottom half to type 2 (both Cu EAM). I ran two cases, which I believe should yield similar results, and minimized both structures:

- No interaction between layers with no create_bonds:
- No interaction between layers with bond_style zero:

For run #1, I get a total energy of -14221.6. For run #2, I get a total energy of -13893.1. Since the models are not being time-integrated, I would assume the two values to be much closer than this. Does anyone know where this additional contribution is coming from?

Thank you in advance,

- Nick

CODE:

# ------------------------ INITIALIZATION ----------------------------

echo screen

units metal

dimension 3

boundary p p p

atom_style full

variable latparam equal 3.615

# ----------------------- ATOM DEFINITION ----------------------------

lattice fcc ${latparam}

region substrate block 0 8 0 8 0 16

create_box 2 substrate bond/types 1 extra/bond/per/atom 6

lattice fcc ${latparam} origin 0 0 0 orient x 1 0 0 orient y 0 1 0 orient z 0 0 1

region box block INF INF INF INF INF 16

create_atoms 1 region box

region bottom block INF INF INF INF INF 8

region top block INF INF INF INF 8 16

set region top type 2

group top type 2

group bottom type 1

mass 1 63.54

mass 2 63.54

atom_modify sort 0 0

# ----------------------- POTENTIAL/BOND ------------------------------

pair_style eam/alloy

pair_coeff * * Cu01.eam.alloy Cu Cu

bond_style zero

bond_coeff 1

# ----------------------- ADD BONDS ------------------------------------

create_bonds top bottom 1 0 3.615

neigh_modify exclude type 1 2

# ----------------------- CHECK BONDS ------------------------------------

compute peBond all pe bond

# ----------------------- MINIMIZE -----------------------------------

shell mkdir dump_bond

shell cd dump_bond

timestep 0.01

thermo 1000

thermo_style custom step etotal ke pe enthalpy c_peBond

dump RELAX all custom 1000 Cu_bond_base.*.cfg id type x y z

min_style cg

min_modify dmax 1.0e-2 line quadratic

fix min all box/relax aniso 0.0 vmax 0.01

minimize 0.0 1.0e-4 10000 10000