I was trying to follow this recipe, NanoCrystal / Graphene Heterostructure in VESTA step by step but instead of an Au nanocrystal, I put a small graphene nanoflake approximately 3.35 Å on top of graphene.
I then put a flake on it, removed repeated atoms on the boundary of graphene, and exported it as an xyz file. When I open this xyz in VESTA, it looks fine:
The number of atoms is also correct: 242 in $11 \times 11$ graphene, 42 in the flake, 284 in the xyz.
Then I made a copy of the POSCAR for $11 \times 11$ graphene, copied there the lines of atom coordinates from the xyz file, changed the number of atoms to 284, removed the C labels, opened it in VESTA, and this is what I got:
Why such a huge number of atoms?
It only extends graphene. The flake is not replicated.
What am I doing wrong?