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I want to start studying some single-atom catalysts doping with a transition metal. However, I do not what protocol I should follow.

Based on the articles that I read, I should dope my surface only after I already optimized my unit cell and created my surface, however, how do I should decide what sites I will choose to make the substitution in my surface?

For example, how to decide that this is the better substitution:

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You are showing an fcc (100) surface, and there is only one type of site to substitute. You want to generate a single-atom alloy (SAA) surface, then it doesn't matter which surface atom you replace with the dopant, because they are all equivalent. Your question is only relevant if it's a stepped surface. In that case, compare the energy of all possible SAA surface configurations, e.g. step-doped and terrace-doped, and go with the lowest-energy configuration.

Generally speaking, there are two important energetics that you need to check for SAA surfaces before everything:

  • Surface mixing energy which evaluates the segregation propensity of each SAA surface w.r.t bulk. The dopant cannot even appear at the surface if it's positive. \begin{equation} E_{\mathrm{mix}} = E_{\mathrm{D}_1\mathrm{H}} + \tilde{E}_{\mathrm{bulkH}} - (E_{\mathrm{H}} + \tilde{E}_{\mathrm{bulkD}}) \end{equation} where $E_{\mathrm{D}_1\mathrm{H}}$ and $E_{\mathrm{H}}$ are the energies of the SAA slab and the pure host slab, respectively, $\tilde{E}_{\mathrm{bulkH}}$ and $\tilde{E}_{\mathrm{bulkD}}$ are the per-atom energies of the bulk host and the bulk dopant, respectively.

  • Aggregation energy which evaluates the aggregation propensity of the dopant atoms forming clusters (e.g. dimers and trimers) on the host metal surface. A dispersed SAA phase cannot be formed if it's negative. \begin{equation} E_{\mathrm{agg}} = E_{\mathrm{D}_n\mathrm{H}} + (n-1)E_{\mathrm{D}} - nE_{\mathrm{D}_1\mathrm{H}} \end{equation} where $E_{\mathrm{D}_n\mathrm{H}}$ are the energies of an alloy slab with a surface cluster of $n$ dopant atoms, $E_{\mathrm{D}}$ is the enenrgy of the pure dopant slab.

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  • $\begingroup$ I hope that whoever downvoted says something, and I hope the OP chimes in too, because so far mine was the only upvote. Was the downvote there when your answer was super short? $\endgroup$
    – Nike Dattani
    Oct 4 at 2:34

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