Creating atoms on lattice points through random distribution

Hi there,

I have a question about the best method for creating and minimizing a two type alloy. In my system, one atom fills the entire simulation box on an fcc lattice and the other atoms sit on the octahedral sites of this fcc lattice, i.e. at another fcc lattice with origin 0.5 0 0 in box units. I previously tried using the “create_atoms random” command for filling the second atom lattice with a certain fraction of atoms compared to the first fcc lattice, and found that due to the amorphous nature of how the random distribution occurred, my system did not fully minimize (some atoms went to other, non-octahedral empty sites or were not exactly at the sublattice points) even when using a very low cutoff parameter set on the minimize command with enough steps to avoid cutoff (minimize 1e-25 1e-25 10000 10000). Is there a way to fill this sublattice randomly within LAMMPS, or should I just create “region” commands that enclose enough of the simulation box in order to include as many of the secondary atoms as I desire? Thanks for the help.

Joseph Serio
M.S. Candidate, NPRE, University of Illinois at Urbana-Champaign

Hi there,

I have a question about the best method for creating and minimizing a two type alloy. In my system, one atom fills the entire simulation box on an fcc lattice and the other atoms sit on the octahedral sites of this fcc lattice, i.e. at another fcc lattice with origin 0.5 0 0 in box units. I previously tried using the “create_atoms random” command for filling the second atom lattice with a certain fraction of atoms compared to the first fcc lattice, and found that due to the amorphous nature of how the random distribution occurred, my system did not fully minimize (some atoms went to other, non-octahedral empty sites or were not exactly at the sublattice points) even when using a very low cutoff parameter set on the minimize command with enough steps to avoid cutoff (minimize 1e-25 1e-25 10000 10000). Is there a way to fill this sublattice randomly within LAMMPS, or should I just create “region” commands that enclose enough of the simulation box in order to include as many of the secondary atoms as I desire? Thanks for the help.

you should be able to create the structure you want by creating the
full lattice with the first type of atoms and then create the second
set of atoms with a custom lattice. of course, now you have atoms
sitting on top of each other, but that can be remedied through using
the delete_atoms overlap option. if you choose your groups and cutoff
wisely, you should end up with exactly the structure you want.

axel.