[Wien] consistent RKmax and sphere size settings

[Laurence Marks]

Have a look at http://www.wien2k.at/reg_user/faq/rkmax.html. If (say) with
an RMT for the N of 1.6 a RKMAX of 6.5 is good enough, then when you reduce
the RMT to 1.3 you can reduce the RKMAX to 6.5*1.3/1.6 = 5.28. This will
not give you precisely the same relative convergence, but is close.

Another way is to say that an RKMAX of 7 is "OK" for RMTs of 2.0, an RKMAX
of 3 for RMTs of 0.5, then interpolate using a straight line. This is
similar.

On Wed, Apr 7, 2021 at 3:24 PM Pavel Ondračka <pavel.ondracka at email.cz>
wrote:

> Dear Wien2k mailing list,
>
> I have a series of TiN and TiON amorphous-like structures where I have
> some large differences in spheres sizes for N atoms. In most of the
> structures the smallest N sphere is around 1.6-1.7, however in some I
> have few N atoms with 1.3 (the structures should be OK, this much
> smaller size is due to some rare local configuration which would
> correspond to something like N split interstitial in crystalline
> structure).
>
> My goal is to calculate core electron binding energies of N1s levels of
> many atoms in the structures (at least 200 core-hole calculations) and
> I need to be consistent over different structures in the series.
>
> So usually I would just check what is the smallest N sphere size in the
> whole set, and force it for all N atoms in all structures and than use
> the identical RKmax for all structures, just to be sure I'm consistent.
> This is unfortunatelly not very efficient with respect to the
> calculation speed as I have quite large cells (around 150 atoms). Is
> there another way how can I save some CPU time and keep the
> consistency?
>
> I was for example thinking if I can force somehow two different N
> sphere sizes (one for the N split intestitial, which I have usually
> just one in the whole cell and one larger for the rest of N atoms),
> than I would have consistent sphere size for the rest of N atoms in the
> series and I could change the RKmax to keep the same largest K-vector
> which should be enough to guarantee consistency for all N atoms expect
> the split interstitials (but I don't care that much about them).
> However as far as I understand this is not possible?
>
> Any ideas would be appreciated.
>
> Best regards
> Pavel Ondracka
>
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-- 
Professor Laurence Marks
Department of Materials Science and Engineering
Northwestern University
www.numis.northwestern.edu
"Research is to see what everybody else has seen, and to think what nobody
else has thought" Albert Szent-Györgyi
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