Is there an option to relax a crystal in the xy direction only without changing the z direction?

[sylvester_makumi]

I am trying to relax a crystal composed of 2D material on a 3D substrate, but I find that the two materials' atoms mix inside the cell so I don't have the 2D sheet anymore. So I am wondering if there is a way to restrict atom movements in the z direction or if there is a better way to relax my crystal.
Again, do we have an option to tell VASP the crystal is a 2D sheet in addition to having a vacuum?

files.zip

[ferenc_karsai]

1) You can restrict the relaxation of the Bravais lattice by using an ICONST file. For the explanation of the ICONST file please read the corresponding wiki page:
wiki/index.php/ICONST

2) You can restrict the relaxation of given atoms by defining "Selective dynamics" in the POSCAR file and by setting "T" or "F" for each coordinate of the atoms in the POSCAR file. This feature is explained on the POSCAR page in the wiki:
wiki/index.php/POSCAR

You can also combine both if needed.

[sylvester_makumi]

Thank you !