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Cross-posted on MMSE.

Is there any evidence that spin-orbit coupling (SOC) leads to significant changes in atomic structure? Using DFT, I am getting different relaxed lattice constants when I take SOC into account compared to when I neglect it. Is this a bug or a feature? Are there any known materials where SOC leads to structural distortion?

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    $\begingroup$ Have a look at Pekka Pyykkö's work. I recommend starting with his great 2012 review, Relativistic Effects in Chemistry: More Common Than You Thought - check out section 4.6. $\endgroup$ Nov 22, 2023 at 12:25
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    $\begingroup$ If there are two states with different symmetry so they do not interact, then you introduce an operator that mixes them the total energy should remain the same with one state increasing the other lowering in energy and locally form an avoided crossing which should, I suppose, change the geometry at the crossing point. $\endgroup$
    – porphyrin
    Nov 22, 2023 at 13:41
  • $\begingroup$ Sure, eg IrO2 is doing it, but it is doing the other way:SOC is needed for higher symmetry models, and the lack of SOC leads to distortion $\endgroup$
    – Greg
    Nov 25, 2023 at 9:44
  • $\begingroup$ @NicolauSakerNeto I remember seeing it and it is great, but now paywalled. I assume we (now) have to pony up? $\endgroup$ Nov 26, 2023 at 22:40
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    $\begingroup$ @OscarLanzi You can find it on ResearchGate here $\endgroup$ Nov 26, 2023 at 23:16

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"I am getting different relaxed lattice constants when I take SOC into account and when I neglect it."

That sounds correct. I would be surprised if the lattice constants remained precisely the same after taking into account spin-orbit coupling.

"Are there any known materials where SOC leads to structural distortion?"

All of them. Unless you're able to show an example in which the lattice constants obtained from theory remain precisely the same after introducing spin-orbit coupling into the model.

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