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I created a CIF file using the experimental parameters of my material, then I used it to create my input file for the unit cell using Cif2Cell. After that, I relaxed the structure using vc-relax.

If I want to create a supercell (of the same unit cell) to introduce a defect, do I have to use the CIF file with experimental parameters to create the supercell using Cif2Cell then relax the structure using vc-relax, or can I directly create a supercell using my input file of the optimized unit cell (without optimizing the supercell)?

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    $\begingroup$ Create the supercell from the optimized unit cell, then after introducing the defect you may relax the supercell. $\endgroup$
    – Sha
    Mar 7, 2023 at 3:27
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    $\begingroup$ Aside from doing a relaxation calculation after introducing the defect, keep in mind that the supercell should be large enough so that there is essentially no interaction between the defect and its images (due to 3D periodic boundary conditions in Quantum ESPRESSO) $\endgroup$ Mar 7, 2023 at 7:04
  • $\begingroup$ @Sha If I have to create the supercell from the optimized unit cell then I have to use the input file. So how to create a supercell from the input file? Because with Cif2Cell you can do that just from the CIF file . $\endgroup$
    – Camilla
    Mar 7, 2023 at 8:23
  • $\begingroup$ Similar questions: here, here, here, and here. $\endgroup$
    – Camps
    Mar 7, 2023 at 18:12

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You can directly create a supercell using your input file of the optimized unit cell without optimizing the supercell. The optimized structure of the unit cell represents the most stable configuration of the crystal, and you can use this optimized structure as a starting point for creating the supercell. Regarding your second question, you can create a CIF file from the SCF output file. For instance, you can open the output file using XCrysDen, save it as .xsf format, and import it into VESTA. From there, you can generate a CIF file.

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