[Wien] setrmt_lapw

[Fecher, Gerhard]

Dear John
I guess the rMTs of Wien2k have not much to do with the rMT you need for LEED
as it for example known from Pendry's LEED codes (KKR type) . 

To calculate the scattering phase shifts you will need to use the complete potential but
in Wien you have an interstitial and you don't know which part belongs to what atom.

KKR is doing that for example in a different way, it does not come with an interstitial but uses
Wigner-Seitz spheres and shape functions to describe the full symmetry potential
(for examples see the code of Hubert Ebert or Jürgen Braun,
check J. Braun, Rep. Prog. Phys. 59, 1267 (1996), but he also has much more recent papers)

Some years ago I tried to convert the potentials but gave up, 
good luck, my best wishes are with you

Ciao
Gerhard

DEEP THOUGHT in D. Adams; Hitchhikers Guide to the Galaxy:
"I think the problem, to be quite honest with you,
is that you have never actually known what the question is."

====================================
Dr. Gerhard H. Fecher
Institut of Inorganic and Analytical Chemistry
Johannes Gutenberg - University
55099 Mainz
________________________________________
Von: wien-bounces at zeus.theochem.tuwien.ac.at [wien-bounces at zeus.theochem.tuwien.ac.at]" im Auftrag von "Peter Blaha [pblaha at theochem.tuwien.ac.at]
Gesendet: Mittwoch, 12. September 2012 15:40
An: A Mailing list for WIEN2k users
Betreff: Re: [Wien] setrmt_lapw

RMTs are NOT set according to ionic radii, smallest potential or charge
density discontinuity,.... (why, we have a full potential anyway !),
but solely by the requirements that the wavefunctions of different atoms in a cell
converge approximately at the same Kmax value (plane wave cutoff).

We know that the convergence in APW goes approximately with RMT * Kmax.
Suppose H converges at RKmax=3, but O requires RKmax=6, then we set the radii as
0.5 and 1.0 for H and O, such that Kmax=6 and R_H * Kmax=3 and R_O * Kmax=6.

These rules have been found empirical by tests.

Am 12.09.2012 14:39, schrieb John Rundgren:
> Dear Prof. Blaha et al.,
>
> Questions about setrmt_lapw:
>
> 1) rmt is generated by perl script setrmt_lapw, which takes data from
> SRC_nn/nn.f written by Schwarz and Blaha in 1988. Is the underlying
> theory described in any publication?
>
> 2) Since "initialize calc." begins from setrmt before setting XC and
> before starting "run SCF", I believe that setrmt is based on free-atom
> Coulombic potentials together with the crystal structure (so that the MT
> spheres do not overlap).
>
> However, another idea is that rmt be determined by the total potential =
> Coulombic potential + Madelung's electrostatic potential + XC
> interaction.
>
> Unfortunately, this would mean that setrmt be a part of "run SCF".
>
> 3) For a test I calculate LEED phase shifts (0-300 eV) for TiO2
> comparing setrmt with a method using total potential [PRB
> 68,125405(2003), Surf.Sci.602,1299(2008)]. The Attached diagram shows
> that the total scattering cross section depends significantly on the
> rmt's.
>
> The diagram is produced using Mattheiss's superposition potential. My
> dream is to use SCF potentials for LEED phase shifts.
>
> I am occupied by a write-up on rmt's and SCF potentials, and I would
> gratefully listen to your comments on the rmt matter.
>
> Best regards,
> John Rundgren
> KTH
>
>
>
> _______________________________________________
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> Wien at zeus.theochem.tuwien.ac.at
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>

--

                                       P.Blaha
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Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
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Email: blaha at theochem.tuwien.ac.at    WWW: http://info.tuwien.ac.at/theochem/
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