[lammps-users] Binding Energy Using LJ

Dear LAMMPS Users

I’m trying to calculate the binding energy between two graphene layers using an LJ potential. I realize there are more accurate descriptions but I’m doing this as an initial step in my research. My problem is in the value of binding energy between the two layers, it does not yield the epsilon value of the LJ potential which is the minimum energy. The code is easily run on two cores and takes less than 10 seconds to reproduce the issue. It also calculates the binding energy. I attached the code and the related files. Your help is very much appreciated.

Kind Regards

input.in (1.33 KB)

c_optimized.tersoff (492 Bytes)

Graphene_sc_10x10.dat (16.1 KB)

You have to explain a bit more in detail what you have in your input and why you expect the energy (which energy) be the epsilon of the LJ interaction.
The LJ interactions are not only between one pair per atom, but each atom has multiple atoms in the opposite sheet that it is interacting with.

just look at this trivial input example:
units metal
boundary f f f
region box block -10 10 -10 10 -10 10
create_box 2 box

variable sigma index 3.0
variable epsilon index 0.05
variable halfmin equal 0.5v_sigma2^(1.0/6.0)

mass * 1.0
pair_style lj/cut 20.0
pair_coeff * * 0.0 {sigma} pair_coeff 1 2 {epsilon} ${sigma}

create_atoms 1 single 0.0 0.0 -{halfmin} create_atoms 2 single 0.0 0.0 {halfmin}

run 0 post no
print “Energy per atom for a single pair with distance (2.0*v_halfmin): (etotal/atoms) epsilon ${epsilon}”

create_atoms 1 single 3.0 0.0 -{halfmin} create_atoms 2 single 3.0 0.0 {halfmin}

run 0 post no
print “Energy per atom for two pairs with distance (2.0*v_halfmin): (etotal/atoms) epsilon ${epsilon}”

create_atoms 1 single -3.0 0.0 -{halfmin} create_atoms 2 single -3.0 0.0 {halfmin}

run 0 post no
print “Energy per atom for three pairs with distance (2.0*v_halfmin): (etotal/atoms) epsilon ${epsilon}”

with six atoms and no periodicity, each atom of type 1 is interacting with three atoms of type 2 and vice versa and only one of those three is at the distance of the minimum of the potential.
with each added pair, the energy per atom has to go up.