Dear Lammps users,

I’m writing this issue as I couldn’t find similar problem to be solved neither on the Lammps community, nor in the manual in details. Briefly, I need to build a FCC structure. However, there is molecules ( each molecule has two atoms ) on the lattice site. For the molecule, the axes of the two atoms is along [ 0 0 1 ], and lets assume that the atomic bond is 0.7 while the lattice constant is 3.75A. The inter-atomic potential between single atoms in the molecules and the inter-molecular potential between molecules need to be defined as well separately.

To generate the structure I used:

units metal
dimension 3
boundary p p p
atom_style atomic

lattice fcc 3.75
region whole block 0 1 0 1 0 1
create_box 1 whole

molecule X2 molecule.txt
region box block INF INF INF INF INF INF units box

lattice fcc 3.75 orient x 1 0 0 orient y 0 1 0 orient z 0 0 1
create_atoms 0 box mol X2 100000001 units box

where molecule.txt is as follows:

2 atoms


1 0 0 0
2 0 0 0.07


1 1
2 1

As for create atoms 0, I understand that it should not be correct. However, It gives error with 1 and 2 ( 1+1 ). So, the final structure that I get has 8 atoms. However, the arrangement of the atoms is not similar to FCC ( knowing that there should be 1 atom in the corner and three at the face for atomic arrangement. Thus I concluded that a similar arrangement should be exist for the molecules. ).
Q.1) Is there anything wrong with the simulations ?
Q.2) Further more, how can I define the potential between the molecules thereafter ? I have tersoff between the atoms and For the sake of simplicity, assume that LJ is applied between the molecules .

Any response would be appreciated.