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I am trying to model the adsorption of charged atom (Zn2+) on the metallic surface using VASP.

Since NELECT assumes total charge (metallic surface + Zn), is it the right flag to use? Or are there any other better methods to define Zn2+ in my structure and calculation?

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  • $\begingroup$ Does the Zn2+ come from an aqueous solution? And, is the metal expected to reduce the Zn2+ to lower oxidation states? $\endgroup$
    – wzkchem5
    May 4, 2023 at 11:13
  • $\begingroup$ Yes, Zn2+ comes from an aqueous solution. $\endgroup$
    – Abhishek
    May 5, 2023 at 12:46

1 Answer 1

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Since you are studying $\ce{Zn^{2+}}$ in an aqueous solution, and the aqueous solution is neutral, there must be counteranion(s), e.g. two monoanions or one dianion, per $\ce{Zn^{2+}}$. The counterions have to be included because periodic calculations require that the unit cell must be charge neutral. Then, once you include the correct number and type of counterion(s), the extra $\ce{Zn^{2+}}$ is automatically divalent (assuming that the metal does not reduce the $\ce{Zn^{2+}}$), and you do not need to do anything else to ensure that.

Another important thing is that, since $\ce{Zn^{2+}}$ exists as $\ce{Zn(H2O)6^{2+}}$ in aqueous solution, you must explicitly consider the water molecules (or maybe some of the counterion(s), depending on which counterion you use) that coordinate directly to the $\ce{Zn^{2+}}$. Moreover, when the counterions have very localized or strong negative charge (e.g. $\ce{Cl-}$ and $\ce{SO4^{2-}}$), it is desirable to explicitly solvate the latter as well. Finally, an implicit solvation model should be added to describe the solvent outside the first coordination shell.

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