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How well can DFT, as implemented in VASP, describe surface reactions?

For example, I want to study the hydrogen evolution reaction (HER) on the $(111), (110), (100) \text{ and } (011)$ surface planes of Cobalt (III) Phosphide $\ce{CoP}$. Assuming I have optimized bare surface geometries, can I expect reasonable energetics for hydrogen production using DFT calculations of the energy and surface bound geometries?

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    $\begingroup$ Challenges compared to what? Compared to other software packages? Compared to reactions other than HER? Compared to other kinds of materials? $\endgroup$
    – wzkchem5
    Nov 22, 2021 at 8:41
  • $\begingroup$ I mean the challenges inherent in using DFT itself. For example, it is known that DFT is not good in finding the band gap of most materials. In this case, what are the possible challenges that could be encountered in using DFT to study the HER of the mentioned Transition Metal Phosphides in general (and the mentioned surface planes of Cobalt (III) Phosphide in particular)? $\endgroup$ Nov 22, 2021 at 10:38
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    $\begingroup$ I see. I know basically nothing about CoP (esp. whether it is a narrow-gap semiconductor or even a metal), but I guess that compared to the intrinsic errors of the DFT method, surface reconstruction and leaching may be even bigger problems. Phosphides are generally labile under acidic conditions (or even in neutral water) and tends to release PH3. While the bulk material CoP may be stable under such conditions, it's hard to say whether there will be one or two layers of the phosphides near the surface that will be leached. And that will make a big difference in the catalysis $\endgroup$
    – wzkchem5
    Nov 22, 2021 at 13:13
  • $\begingroup$ Thank you very much @wzkchem5 for your response. Any other persons with helpful insights should kindly post their answers please. Thanks $\endgroup$ Nov 23, 2021 at 14:26
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    $\begingroup$ @thehereandnow There's plenty of challenges when using DFT. Maybe it would help if you could tell us why you're interested in knowing what the challenges are? $\endgroup$ Dec 25, 2021 at 21:17

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Your initial question is quite broad, and there are many sub-questions that DFT calculations may or may not be able to answer. For example, DFT is useful for studying trends in reaction kinetics vs. reactivity of materials. There are many examples of this in literature.

For example, trends in calculated surface reactivity across metal phosphides correlated with observed HER kinetics: https://pubs.rsc.org/en/content/articlelanding/2015/ee/c5ee02179k

It is harder to be confident in getting "reasonable energetics", as you put it, for a particular adsorption thermochemistry. Trends and differences in adsorption thermochemistry have often been found to be insightful, as in the linked study. This is a bit of a broad answer to a broad question.

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