[Wien] N1s binding energy in TiN

[Pavel Ondračka]

On Thu, 2019-01-17 at 09:28 +0100, Peter Blaha 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.

>From my current testing the supercell effect (the core-hole interaction
with its periodic images) is minimal for the TiN, e.g. the N1s binding
energy difference between 8 atoms and 216 atoms is only about 0.1eV (at
similar other parameters). The screening of the core hole is very good
here (at least for the TiN but probably also in other metals, from my
testing cells around 64 atoms are reasonably converged). This is ofc
completely different story for insulators... 

What I saw was that during my testing the difference between the small
8 atom cell with default parameters and the 216 atoms cells with well
tweaked numerical parameters was below 0.2eV. Basically the only input
which has any significant difference is the functional. Which made me
think that maybe I'm missing some secrest ingredient. Probably not...
:-)

> 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.

Right, the main problem with the core-eigenvalues is not that they are
shifted in absolute values but rather they show almost no chemical
shifts, which only become visible when the core-hole is added. The 1-
2% 
is also what I see here and in general is reasonable, I was just
wondering if I could do better.

Best regards
Pavel