[Wien] setrmt_lapw

[Laurence Marks]

Using Wien2k for LEED potentials is an interesting concept -- it has
been used fairly extensively for TED potentials and there are some
differences between the self-consistent potential and the independent
atom potentials as I am sure you know; you can find some papers on the
Wien2k webpage by John Spence and others.

However, the rationale for the RMT in setrmt is quite different from
that for a LEED calculation. The RMTs are an attempt to balance having
the core electrons well confined for each different type of atom,
avoiding overlap of RMTs and also having them as large as possible as
the basis set within the RMTs is rather good so they converge faster.
Peter can probably comment about the latest version (I think it
changed) but I suspect that his comments will be more that it is
"close to best based upon tests".

There is nothing "magic" about the values from setrmt, and in fact on
a case-by-case basis one can perhaps do better. More importantly, I
don't think that they connect to what is used in LEED in any simple
fashion -- they depend upon the electron density not the potential as
you have written. It would be incredibly complicated to adjust the
RMT's during a calculation, many things would need to be rewritten,
i.e. quite a few woman-months.

I think you should target a code to convert "somehow" the WIen2k
converged potential (with XC or perhaps without -- why use XC?) to a
form that you want. You will have to worry about things like the
derivative discontinuity with APW+lo.

On Wed, Sep 12, 2012 at 7:39 AM, John Rundgren <jru at kth.se> wrote:
> 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
>



-- 
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