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If I have a CIF that is P1, is there a (preferably free) code that can map the structure to some user-specified space group? I know that there are ways to do similar things with molecular systems. For instance, ChemCraft has an option to detect the nearest point group and then apply it to the molecule. I'd like to do the same for a crystalline structure given a space group.

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  • $\begingroup$ Do you mean, identifying underlying symmetry of the crystal? $\endgroup$ – Thomas May 2 at 2:17
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    $\begingroup$ I primarily mean updating the atomic positions to fit a given space group. While it'd be nice if the code can detect the closest symmetry, that is not a requirement. For instance, let's say you have a DFT-optimized structure. It'll probably have no symmetry unless the tolerances to detect the symmetry are somewhat loose. Are there codes that could map the structure to match a given symmetry? $\endgroup$ – Andrew Rosen May 2 at 2:21
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    $\begingroup$ As an aside, I know this can be done in Materials Studio, but that's paid software. For context to my question, my machine with Materials Studio is in lab, which I can't access because of the global pandemic, so I'm looking for an alternative... $\endgroup$ – Andrew Rosen May 2 at 2:24
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While there are undoubtedly other programs that do this, it's fairly easy to do in Avogadro.

  • I start with a calculation on hexagonal SiC. As mentioned, it starts as $P_1$:

triclinic setting of a non-ideal SiC unit cell

  • Go to Crystallography -> Space Group -> Perceive Space Group

Avogadro menu item for Perceive Space Group...

  • The unit cell should update, including symmetrization if needed

enter image description here

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    $\begingroup$ Beautiful, thank you! I admit... I am feeling quite silly that I didn't realize this! I'll keep the question unanswered for now so others feel inclined to comment too. $\endgroup$ – Andrew Rosen May 2 at 4:05
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    $\begingroup$ It's a fairly common task - I don't know other materials builders well, but I suspect others can do this. $\endgroup$ – Geoff Hutchison May 2 at 4:11
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This can be done using PyMOL (which, while not free for general use, does have a free student license) via the set_symmetry argument, as documented here. This allows for a user-specified spacegroup and will update the CIF to match.

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    $\begingroup$ PyMOL also has Open Source version, which is free for all users and has set_symmetry. $\endgroup$ – marcin May 5 at 17:03

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