[Wien] setrmt_lapw
Laurence Marks
L-marks at northwestern.edu
Fri Sep 14 15:07:36 CEST 2012
So long as the RMTs do not overlap you can use whatever you want, with
caveats that you will need to verify that you are getting appropriate
convergence/densities. You will also need to be careful about what
states you force to be core and core leakage (:NEC in case.scf). There
are many plausible ways of checking, one is the heat of formation of
compounds another is band-gaps, i.e. compare what you get to more
standard values. With a large enough RKMAX you will probably be OK,
but you will have to test carefully. Peter can probably suggest
other/better tests to ensure that the "LEED appropriate" RMTs are not
creating problems.
One important caveat: beware the derivative discontinuity at the
muffin tins. My intuition is that this might give you incorrect phase
shifts. You may need to go beyond the normal LM of 6 to 8 or 10
and/or check with just LAPW (as against APW+lo) and higher RKMAX.
(The unsupported utility RMTCheck will let you monitor these.) One of
my students put together a version of symmetry to go to 8 or 10 which
I can provide if needed although I do not warranty that it is safe.
Also, the high-angle terms might be an issue; it is know that Wien2k
does not give as good values for the high-angle x-ray scattering
factors as (for instance) Gaussian. I don't know if this will matter
but it could because (I think) the LEED Ewald sphere has large g
backscattering terms.
A standard test (for TED) is to compare the dstart densities with what
one gets from the tabulated x-ray or electron (e.g. Doyle-Turner)
scattering factors. They should agree, and I suspect they should be
comparable for LEED although I only know enough to be dangerous.
On Fri, Sep 14, 2012 at 7:17 AM, John Rundgren <jru at kth.se> wrote:
> Dear WIEN2k Team,
>
> Thanks for setrmt_lapw info posted by Laurence, Peter, Gerhard, and
> Peter, in order of emails appearing on my screen.
>
> Peter's second info is glowing hot: "extend the potential from RMT onto
> some larger sphere (e.g. a WS sphere)". Such an extension is exactly
> what is desirable for the application of WIEN2k to LEED scattering phase
> shifts.
>
> New inquiry: How is such an extension made? Is a piece of code available
> somewhere in W12.1?
>
> My phase shift code has an entrance for case.clmsum and case.vcoul as
> is. But for comparison of WIEN2k's self-consistence with Mattheiss's
> direct superposition I need freedom of manipulation to greater radii
> than those delivered by setrmt_lapw.
>
> With best wishes,
> John
> KTH
>
>
> On Thu, 2012-09-13 at 22:59 +0200, Peter Blaha wrote:
>> I do not know what exactly you need, but just a remark:
>>
>> One can expand the interstitial potential (fourier series) into Besselfunctions
>> from any center and thus "extend the potential from RMT on to some larger sphere (e.g. a WS sphere)
>>
>> Am 13.09.2012 22:54, schrieb 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
>> >>
>> >>
>> >>
>> >> _______________________________________________
>> >> Wien mailing list
>> >> Wien at zeus.theochem.tuwien.ac.at
>> >> http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
>> >>
>> >
>> > --
>> >
>> > P.Blaha
>> > --------------------------------------------------------------------------
>> > Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
>> > Phone: +43-1-58801-165300 FAX: +43-1-58801-165982
>> > Email: blaha at theochem.tuwien.ac.at WWW: http://info.tuwien.ac.at/theochem/
>> > --------------------------------------------------------------------------
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>>
>
>
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--
Professor Laurence Marks
Department of Materials Science and Engineering
Northwestern University
www.numis.northwestern.edu 1-847-491-3996
"Research is to see what everybody else has seen, and to think what
nobody else has thought"
Albert Szent-Gyorgi
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