[Wien] calculation of binding energy

[Peter Blaha]

Of course one MUST NOT simply look at the core eigenvalues and compare them
with experiment. There are two reasons behind,
i) The energy zero, which will be different for different calculations.
You can try to get the "trends" right, when comparing the E-differences 
between the core state and EF (and consider the experimental workfunction,
which might also contribute when different for different compounds).
 
ii) DFT eigenvalues are in principle NOT the ionisation energies which you 
measure in experiment. Errors of more than 10% are typical.

To overcome this, you have to do either "Slater's transition state" or
"delta-SCF" calculations. For both methods you have to create a core hole
(half a core hole for Slaters t.st.) and do a calculation with this
core hole (change inc manually, add this electron in the valence (in2); 
eventually break symmetry or generate a small supercell so that the core 
hole is just on one of the atoms). Then you look at the eigenvalue (Slater) 
or at the total energy differences.

I guess there are several papers on core-level shifts with WIEN in literature.
Relative shifts should be quite precise, absolute binding energies have errors
of 1% (if I remember correctly).

> I am trying to compare experimental (XPS) binding energies to calculations for
> S atoms in different Ni sulfides with different structures and co-ordination.
> 
> The core state energies calculated by Wien are quite different from experiment
> and FEFF8 calculations. I assume this is because the zero in the Wien
> calculations is the average Coulomb potential not the the vacuum level. We are
> also seeing that the trends in the core level energies are different for Wien
> than experiment and FEFF.
> 
> Does anyone have any advice on how to go about comparing calculated and
> experimental binding energies and also on how reliable we might expect them to
> be?
> 
> Thanks and best wishes to you all,
> 
> Regards
> Vicki
> 
> -- 
> --------------------------------------------------------------------------------
> ---
> Dr. Vicki J. Keast
> Australian Key Centre for Microscopy and Microanalysis
> Madsen Building F09
> University of Sydney
> Sydney NSW 2006
> Ph: + 61 2 9351 4523
> Fax: + 61 2 9351 7682
> email: v.keast at emu.usyd.edu.au
> 
> For correspondence regarding the Australian Microscopy and
> Microanalysis Society, please reply to amms.secretary at emu.usyd.edu.au
> --------------------------------------------------------------------------------
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> 
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                                      P.Blaha
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Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
Phone: +43-1-58801-15671             FAX: +43-1-58801-15698
Email: blaha at theochem.tuwien.ac.at    WWW: http://info.tuwien.ac.at/theochem/
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