[Wien] Poisson and clmsum

[Laurence Marks]

APW+lo methods have a step in the gradient of the density at the RMT. To
avoid this use a lapw basis set: to reduce it increase RKMAX.

---
Professor Laurence Marks
"Research is to see what everybody else has seen, and to think what nobody
else has thought", Albert Szent-Gyorgi
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Co-Editor, Acta Cryst A


On Nov 21, 2016 07:39, "John Rundgren" <jru at kth.se> wrote:

> Dear Peter Blaha and Gavin Abo,
>
> Non-overlapping muffin-tin spheres are used by WIEN2k and my LEED program
> eeasisss (Elastic Electron-Atom Scattering in Solids and Surface Slabs).
> But RMT(setrmt_lapw) is not automatically the best choice for
> RMT(eeasisss). LEED touching radii of atoms depend on exchange-correlation
> interaction between crystal electron gas (the WIEN2k electrons) and an
> incident LEED electron (energy 20-500 eV).
>
> This is a N+1 electron scattering situation, where "N" signifies the
> WIEN2k electrons and "1" an alien LEED electron.
>
> W2k can be reconciled with LEED using an atomic sphere approximation (ASA)
> extending into the Fourier expansion realm of W2k. A while ago you (P.B.
> and G.A.) suggested an ASA routine, in which I now use Poisson
> differentiation of vcoul_ASA in order to obtain clmsum_ASA. I consider the
> case LM=(0,0), sufficient for current LEED.
>
> The considered structure is a supercell = a surface slab 15 layers thick,
> where layers 1-2 and 14-15 are C-O and O-C, respectively. Mirror symmetry
> about layer 8. At the C-O layers vcoul_ASA(0,0) is continuous across the
> RMT radius, but clmsum_ASA(0,0) versus radius shows a step of the order of
> 10%.
>
> Is the step k-point dependent? It does not seem so. With 16 and 48
> k-points the clmsum_ASA(0,0) steps are preserved within 6 digits.
>
> I shall be glad to supply the code. When the described numerical error is
> fixed, WIEN2k and eeasisss can be re-run self-consistently within the model
> of non-overlapping muffin-tin atoms.
>
> Regards,
> John Rundgren
>
> KTH
>
>
>
>
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