Dear All,

I use LAMMPS version: lammps- 7Aug, 2019. I downloaded it from lammps website.

I was having difficulties replicating the values of potential energy of the system using the theoretical calculations and LAMMPS. I did it for three different systems. To do a sanity check, I tried to get the output of pair potential values for all the systems used, to my surprise these values were different from what was given in all the potential file.

I tried to calculate the potential energy for a 2 atom system which is described as:(For simplicity, I have shown only one of the input atom coordinates)

FeNiCr:

2 atoms

3 atom types

0.0000 5.0035 xlo xhi

0.0000 5.0035 ylo yhi

0.0000 2.3586 zlo zhi

Masses

1 55.845

2 58.6934

3 51.9961

Atoms

1 1 0.0000 0.0000 0.0000

2 1 2.87056 0.000 0.0000

The potential files were downloaded and replicated for research purposes from:

https://www.ctcms.nist.gov/potentials/

The LAMMPS input format looked like the following:

# Find minimum energy fcc configuration

# Mark Tschopp, 2010

# ---------- Initialize Simulation ---------------------

clear

units metal

dimension 3

boundary s s s

atom_style atomic

read_data atoms1.dat

# ---------- Create Atoms ------------------

# ---------- Define Interatomic Potential ---------------------

pair_style eam/alloy

pair_coeff * * FeNiCr.eam.alloy Fe Ni Cr

pair_write 1 1 5000 r 0.00112 5.6 table.txt RITEEEESH

neighbor 2.0 nsq

neigh_modify every 1 delay 10 check yes

# ---------- Define Settings ---------------------

compute eng all pe/atom

compute eatoms all reduce sum c_eng

# ---------- Run Minimization ---------------------

reset_timestep 0

thermo 10

thermo_style custom step pe lx ly lz press pxx pyy pzz c_eatoms

dump 1d all cfg 1000 dump1.all.*.cfg mass type xs ys zs fx fy fz id type c_eng

min_style cg

minimize 1e-25 1e-25 50000 100000

variable natoms equal “count(all)”

variable teng equal “c_eatoms”

variable length equal “lx”

variable ecoh equal “v_teng/v_natoms”

print “Total energy (eV) = {teng};"
print "Number of atoms = {natoms};”

print “Lattice constant (Angstroms) = {length};"
print "Cohesive energy (eV) = {ecoh};”

print “All done!”

I did similar calculations for different systems using the following potential files with 2 atoms system shown above. But with different spacing which was chosen by critically evaluating the position values used in the reference which was again found at the nist repository:

Ag_Zhou04.eam.alloy

FeNiCr.eam.alloy

Al99.eam.alloy

Unfortunately, by using the following EAM method formula and the values of the pair-potentials, charge density and embedding function from the reference, the values that I get for potential energy is different from LAMMPS:

I have to format the EAM potential for the system which I am creating right now. Therefore, I want to make sure I understand how the LAMMPS algorithm is calculating the given values of potential energy.

I really appreciate your help. If you need any other information from my end, please, don’t hesitate to reach me out at: [email protected]…2061….

Thanks.

Best,

Ritesh

Thanks.