[Wien] binding energies

[fecher]

The answer is simple, XPS does not measure the ground state binding energies. 

This is not just the problem of the N to N-1 electron transition alone (in the 
sense of calculating just the two cases, ground and excited), but will also  
depend , to say in not too physical words, on "secondary" effects some known 
as "multiplett" effects, some as "shake up",  "shake down", etc. as found in 
textbooks of corelevel photoemission (see.: e.g. reviewing articles by Chuck 
S. Fadley and others). The results of calculations may strongly depend 
whether one uses sudden approximation or adiabatic approximation. 
Calculational results may also strongly depend how sorrowly the transition 
matrix elements are calculated.

With FEFF, the result will depend which potential you use and this is most 
probably not the same like the one from Wien2k, so it is no wonder that the 
energies and trends will be different.

The problem of comparing calculated and measured photoemission spectra is, to 
my knowledge, not completely attacked for the most general case, as this is a 
very complicated many-body problem. However, FEFF seems to be a very advanced 
one.


Ciao Gerhard


Am Donnerstag, 16. Dezember 2004 00:37 schrieb Vicki Keast:
> Dear fellow Wien2k users,
>
> 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