[lammps-users] hcp 111 gold surface, how to define best to get the smallest periodic unit?

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1

Dear all,
I’m at a bit of an impasse with a problem regarding 1 1 1 surfaces: I tried to create a 1 1 1 surface by using the fcc lattice and rotating it in order to align the 1 1 1 face with the xy plane and one of the vectors of the hexagonal surface lattice with the y direction

lattice fcc 4.08 orient x 2 -1 -1 orient y 0 1 -1 orient z 1 1 1

to create a periodic box of minimum periodicity I need to set the x size as 3 in lattice coordinates.
I have to deposit a superlattice with a periodicity of 4 by 7 in terms of hexagonal ssurface vectors unfortunately that means that I have to define a very large periodic box in the x direction to get both periodicity of the substrate and the superlattice to be correct.

Am I going at this the wrong way? Is there a better way to define the simulation box so that I get a smaller system that satisfies periodicity?

Thank you,
Mattia Siviero

2

If you have incommensurate lattices and systems where the box size for exact periodicity is very large, you may have to consider tweaking the lattice constants a little bit.
However, this will come with some margin of error, thus you will have to decide which error is dominant in your model.