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How to calculate ionization energy for an alloy system (for eg. $\ce{Mg17Al12}$) using DFT?

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    $\begingroup$ By "ionization energy" do you mean the work function? AFAIK the term "ionization energy" is only defined for finite systems $\endgroup$
    – wzkchem5
    Sep 21 at 17:57
  • $\begingroup$ That was my actual confusion, I know how to find work function but not sure about ionization energy for an alloy. Can you provide some reference that ionization energy is only valid for single element not for alloy? $\endgroup$ Sep 21 at 18:17
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    $\begingroup$ The Wikipedia page says that ionization energy is "the minimum amount of energy required to remove the most loosely bound electron of an isolated neutral gaseous atom or molecule". Whether or not the material is a pure element is irrelevant; the point is that ionization energy is only defined for gaseous matter. So e.g. pure iron metal also doesn't have an ionization energy, only iron atoms in iron vapor do. $\endgroup$
    – wzkchem5
    Sep 22 at 7:53
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Ionization energy is more appropriate for isolated atoms, you want the workfunction or ionization potential of your alloy surface. You calculate this usually from slab calculations because there is explicit vacuum. Work function is defined as:

$$\Phi=E(vacuum)-E(Fermi)$$

If you use vasp this can be useful https://github.com/WMD-group/workfunction

And a very precise example in quantum espresso is available here: https://gitlab.com/QEF/q-e/-/tree/master/PP/examples/WorkFct_example

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