[Wien] N1s binding energy in TiN

[Pavel Ondračka]

Dear Wien2k mailing list,

I'm looking for some advice regarding the calculation of core level
binding energies (to compare with XPS experiments). First of all there
is this nice lecture where prof. Blaha actually shows some calculations
http://susi.theochem.tuwien.ac.at/reg_user/textbooks/WIEN2k_lecture-
notes_2011/Blaha_xas_eels.pdf of core levels with perfect results. For
example with TiN the deltaSCF method gets 397.1eV for the N1s level as
compared to 397.0eV experiment. The trouble is that I'm not able to
reproduce this.

I've done some calculations before and I was never really happy with
the absolute values which were always few eV off but I've always
thought this is just the limitation of xc functional or methodology.
Hence seeing the nice results in the lecture surprised me. However, I'm
not able to reproduce the values even for metals from the example. For
the TiN I'm getting values of 404.8eV with the slaters transition state
approach and 404.6eV with delta-scf (here I'm using the formula for
metals E_b = E^tot_initialstate(N) - E^tot_finalstate(N), i.e. placing
the core-electron in the valence band and with PBE). I have thought
that this is maybe functional difference, since while taking LDA
instead of PBE shifts the results differ almost by 4eV (to 400.9eV).
However with the PBE I get the core energy ε_i as 377.4eV (consistent
with the mentioned pdf where it is 377.5eV) so maybe this is not just
about functional?. I've already checked convergence with supercell size
as well as numerical parameters and I'm actually out of ideas.

To be honest, I'm not much concerned personally about the discrepancy
since the chemical shifts seem to be reasonable even if the absolute
values are not. I just think that if it is possible to get the absolute
values right (or at least closer to experiment) as in the lecture pdf,
the results would of course look way better, therefore I'll be grateful
for any comments and help.

Best regards
Pavel