## Final-state approximation

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Newbie
Posts: 3
Joined: Wed Jul 01, 2020 2:34 pm

### Final-state approximation

Hello,

I am going to calculate core level binding energies of some molecules on metal surfaces by final state approximation. The molecules have number of atoms for different elements. For example for C1s, I have 10 C atoms in the molecule. I can set the calculation to excite core electrons for all C atoms in one calculation or do it one by one in separate calculation by isolating one atom from the rest each time. I tried both way, and I see that there are changes in the calculated fermi level and also the core level energies. However, the trend of calculated core level binding energies is the same by the two approaches. I've read recommendations in some tutorials about doing the calculation separately for atoms of each element.
Is this necessary even when we are interested in getting the core level binding energies of all atoms of one element in the system? or both way is correct?

Kind regards,
Mahsa

alexey.tal
Global Moderator
Posts: 185
Joined: Mon Sep 13, 2021 12:45 pm

### Re: Final-state approximation

Hi,

Usually in the final-state approximation, only one core-hole is created (one excited atom). If you get different binding energies for different atoms of the same species, it is probably because they have different local environment.

Newbie
Posts: 3
Joined: Wed Jul 01, 2020 2:34 pm

### Re: Final-state approximation

Hi,

Is it also correct if I do not create core hole one by one for the same species and do all of them at once?
By different binding energies, I meant the binding energies of certain atom whether the core hole created only for that atom or for all of the atoms of the same species at once, are different.

alexey.tal
Global Moderator
Posts: 185
Joined: Mon Sep 13, 2021 12:45 pm

### Re: Final-state approximation

Exciting multiple atoms simultaneously will cause interaction between excited atoms which should be avoided when simulating the excitation process of core electrons.

Regarding the difference in the binding energies, you should also keep in mind that it is only meaningful to compare the shifts of the binding energies, not the absolute values.