Dear all,
My question is about the correct arrangement of layers for making a slab model in VESTA for adsorption studies.
In the attachments 2 and 3, I tried to build two slab models from the perovskite material SrTiO3 (attachment 1) with two different terminations. I always get the arrangement of atomic layers that the bottom layer is identical to the uppermost layer (due to periodic boundary), and the first layer facing the vacuum (the one necessary for adsorption) is different than the bottom and uppermost layers.
My question is whether this ordering of layer is appropriate or; the bottom layer, the first layer facing the vacuum and the uppermost layer should be the same? If the later is the case, can you provide insight on how to do it in VESTA?
Best regards
As noted by the OP, the bottom layer and uppermost layer in the unit cell model shown are, in fact, the same layer due to PBC.
For many materials, for any geometrically and stoichiometrically correct slab model, the top and bottom of the slab will expose different layers. It depends on the symmetries present in the bulk material. For SrTiO3, formation of a slab with the orientation shown in the images of the OP produces one SrO surface and one TiO2 surface. For a cell with the correct stoichiometry, the top and bottom surfaces of the slab will always be different.
Translationally symmetric layers in adjacent cells must be the same. The two surfaces of a slab may or may not be the same, depending on the symmetries present in the bulk material.
You asked if this ordering is appropriate - well, appropriate for what? What are you trying to do/calculate? To add to the previous answer - you can create slabs with the same surface termination in case the stoichiometry of the layer is not important for your calculation. I recommend to look into the Python package pymatgen which has a built-in function to create surface slabs of all possible terminations and orientations.
Thank you Prof Karl Sohlberg Dr. Peter Schindler and Dr. Hamed Salimkhani for your answers and suggestions.
VESTA is more of a visualization software. You can easily build slab with Materials Studio:
https://youtu.be/mivNb_pFSY4