[Wien] consistent RKmax and sphere size settings

[Pavel Ondračka]

Thank you Laurence,

I was a bit worried because the FAQ you linked also says: "Of course
you should use identical Mg+O spheres for MgO and Mg(OH)2 for
consistency", so I was not 100% sure if keeping the same maximum K-
vector Kmax is enough.

Should I also increase lmax and lvns for the larger spheres somehow? Or
would you keep it the same for small and large N spheres?

Best regards
Pavel

On Wed, 2021-04-07 at 15:33 -0500, Laurence Marks wrote:
> 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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