# concept and uses

Making DFT calculations for bulk crystals is fine, but many properties of real materials arise due to impurities and defects. Or are due to layering. How to deal with that? For periodic DFT codes, the answer is: supercells.

Optional: we describe in this course the use of cif2cell for the generation of supercells. If you want to do more complex tasks such as distributing alloying elements over a supercell in ways that are guaranteed to be symmetry-inequivalent, there is a nice piece of software called ‘supercell’ too that can do this job. It can be installed in your virtual machine. Check the corresponding paper, the website, or the tutorial. You don’t need it for this course, but it can be useful later if you want to dive deeper into this.

Use the tools in or around your favourite DFT code (or read the supercell instructions in the let’s play section) to create a cif-file for the following situations (these are the same exercises as listed in the supercell instructions in the “let’s play” module ):

• Create a supercell for a single atom vacancy in ferrite.
• Create a supercell for a carbon atom that is a diluted octahedral interstitial impurity in ferrite.
• Create a supercell for a (100) and a (110) surface of ferrite, and demonstrate that the atoms in the surface layer in both cases have a different nearest neighbour surrounding.
• Create a supercell with a (110) surface for ferrite, where (a) one of the surface atoms is replaced by another element, and where (b) an impurity atom is added on top of the surface.
• Create a supercell for a (001)-surface of the NaCl crystal, having 7 layers in the slab and some amount of vacuum, with a Si atom on top of the surface (at a lattice position where in the infinite NaCl crystal a Na or Cl atom would be). Periodic images of the Si atom should be 4 lattice parameters away from each other in the horizontal direction.

In all cases, describe how you did it and add a picture (screenshot) of the supercell you made. Put everything in one pdf, and upload it. This task is about creating supercells only, no DFT calculation is needed.

expected time: 1h30m
report time spent (page code AW09A)

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