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In order to model an interstitial trapped in a metal lattice, and the associated incorporation energy, which should be used - "relax" or "vc-relax"? I want to understand the lattice expansion from the interstitial, and that tells me vc-relax, while i realize that an interstitial introduction would involve some lattice strain which would suggest relax.

I was using the energy difference $E_{\rm intAinM} = E(M+A)-(E(M)+E(A))$ to calculate interstitial incorporation energy from both, and they are not the same as one would imagine.

I would love you hear some suggestions or insights into this.

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    $\begingroup$ By interstitial incorporation are you considering the interstitial entity to be an impurity? $\endgroup$
    – Anoop A Nair
    Dec 1, 2020 at 11:18
  • $\begingroup$ Yes. As in a light element (C, H, N or O) in a metal lattice. $\endgroup$
    – Dr.Viper
    Dec 2, 2020 at 3:32

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You should use a large enough supercell such that the effect of vc-relax and relax are negligible. This means that the strain due to the impurity is local.

The following paper provides a comprehensive review on defect calculation in DFT.

https://journals.aps.org/rmp/abstract/10.1103/RevModPhys.86.253

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  • $\begingroup$ Thank you for the answer and the reference. I will read it. As a side, may I ask your views about the supercell size used by this study - aip.scitation.org/doi/10.1063/1.4906047 $\endgroup$
    – Dr.Viper
    Dec 2, 2020 at 3:42
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    $\begingroup$ I think it should be sufficient. $\endgroup$
    – liuyun
    Dec 4, 2020 at 12:51
  • $\begingroup$ Thank you for your time and comment. $\endgroup$
    – Dr.Viper
    Dec 5, 2020 at 15:44

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