When dealing with 2D materials and monolayer families like : transition metal trihalides, TMDCs,...etc. In which cases SOC should be included in our calculations ?

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    $\begingroup$ Here's a very related question: mattermodeling.stackexchange.com/q/169/5. I've removed the part where you ask what SOC is, because that should be a separate question. Also, to make this question look a bit better, can you add anything more to it? Right now the title and the body are the same! For example, perhaps you could write down what you've discovered so far, based on your own research. Doing your own research is typically a mandatory requirement before asking a question on SE. $\endgroup$ Sep 3, 2021 at 20:46
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    $\begingroup$ The question still appears to be broad, are you in bulk properties of materials or molecular solids? Again, if you're interested in exotic cases like 2D materials then its would be different. Usually, SOC comes into picture when there are relativistic effects and, they could possibly have some consequences on magnetic properties of material. You would have to be a little more specific. $\endgroup$
    – user784
    Sep 7, 2021 at 5:35
  • $\begingroup$ I have made some changes of the question. $\endgroup$
    – Chi Kou
    Sep 7, 2021 at 13:06

1 Answer 1


Spin-orbit coupling scales as $Z^4/n^3$ where $Z$ is the atomic number and $n$ is the principal quantum number. When you move down the periodic table and the nucleus becomes heavier and heavier, relativistic effects become more important.

From a practical approach, when should you start incorporating SOC in your DFT calculations? From my experience, that cut-off has been Sulphur (Z=16). It's a good idea to perform a calculation with SOC turned on and investigate the results - if the difference is minimal, you can safely exclude SOC in your calculations. For me, this threshold is similar to the one I adopt for self-consistent calculations when testing different plane-wave cutoffs - Does the total energy of the system change by less than 10 meV/cell between non-SOC and SOC included cases? If so, I would safely ignore SOC. But I must provide a disclaimer here: I'm talking strictly in the context of electronic structure calculations - there could be other properties you could be interested in or exotic behavior such as in the case of Topological insulators.

  • $\begingroup$ Thanks a lot @Xivi76 that's the answer that I was looking for. $\endgroup$
    – Chi Kou
    Sep 11, 2021 at 18:29
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    $\begingroup$ Glad I could help! $\endgroup$
    – Xivi76
    Sep 12, 2021 at 16:55

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