[Wien] N1s binding energy in TiN

Thu Jan 17 09:46:59 CET 2019

My three cents. I think an agreement of 0.1eV should be considered as
fortuitous. There are many issues which are glossed over even with the
miraculous exact functional:

1) The Slater method is a very clever use of the mean value theorem for an
integral. However, it is only 1 value. You can check the literature, I
remember seeing papers where people use a range of holes to more accurately
do the integral.

2) The simple dft-based calculations assume that the final states are plane
waves. Rigorously the exiting photoelectron in XPS is an evanescent Bloch
wave (for a crystal). There is literature on this, but I doubt that it has
been combined with DFT.

3) In experiments you have to worry about photoelectron diffraction, and
there will be some shifts to higher apparent binding energy due to phonon
inelastic scattering. And you have to worry about charging and band bending
for insulators, chemisorption induced work function changes (how clean is
your XPS?)....

_____
Professor Laurence Marks
"Research is to see what everybody else has seen, and to think what nobody
else has thought", Albert Szent-Gyorgi
www.numis.northwestern.edu

On Thu, Jan 17, 2019, 02:29 Peter Blaha <pblaha at theochem.tuwien.ac.at wrote:

> Sorry for the confusion. The quoted values in the pdf are probably from
> a lousy calculation and are ment only to demonstrate the effect (if I
> remember correctly, only a 4x bigger P supercell, but for sure not
> converged, I also don't remember which functional, ....) and only
> accidentally match experiment.
>
> My general experience is that core-eigenvalues (taken with respect to EF
> !!) are 10-15% off, while slater TS gives 1-2 %, i.e. an order of
> magnitude better.
>
>
> On 1/17/19 9:15 AM, Pavel Ondračka wrote:
> > 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
> >
> https://urldefense.proofpoint.com/v2/url?u=http-3A__susi.theochem.tuwien.ac.at_reg-5Fuser_textbooks_WIEN2k-5Flecture-2D&d=DwIGaQ&c=yHlS04HhBraes5BQ9ueu5zKhE7rtNXt_d012z2PA6ws&r=U_T4PL6jwANfAy4rnxTj8IUxm818jnvqKFdqWLwmqg0&m=tkgGA6DHWOQZpcOauDl3Lx8BZ_vGdV0W35tV5es6rQw&s=RWPHx3CucXJZx8K7anGE8WYmvRBxkjijDa1up4sQ7Rg&e=
> > 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
> >
> >
> >
> >
> > _______________________________________________
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> >
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>
> --
>
>                                        P.Blaha
> --------------------------------------------------------------------------
> Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
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