[Wien] vcoul

[Laurence Marks]

What I would do is use lapw3 to generate the x-ray structure factors
then convert using the Mott formula and do a FFT (or use the structure
factors as they are). This is right. We have used this in the past for
TED/HREM data, and personally I trust this a bit more than the Poisson
equation solution, and you can easily include an isotropic temperature
factor for all atoms. (Anisotropic would need an average over
positions (e.g. look at Physical Review B61 (2000) 2506-2512 and
Sergei Dudarev's papers at
http://www.materials.ox.ac.uk/peoplepages/dudarev.html ).

N.B., you need to ensure that you do not have discontinuities at the
RMT, so larger LM's than standard and perhaps a higher RKMAX than 7
are advisable. You can use RMTCheck on the contributed software page
to check.

2011/11/29 John Rundgren <jru at kth.se>:
> Dear Wien2k Team,
> This is about vcoul(L,M=0,0) generated by Fe3O4 and Sr3Mn2O7. I compare
> two potential curves as functions of radius R:
>
> (1) VC(R)=vcoul00(R)/sqrt(4*pi), spherically symmetric;
> (2) VCpois(R), spherically symmetric, obtained from clmsum00 and
> Poisson's equation (using subroutine charg2.f). My boundary condition of
> PE is the conventional one giving zero VCpois for a neutral muffin-tin
> and large R.
>
> In summary, I expect that VC and VCpois are equal up to a constant,
> individual for individual atoms depending on the SCF boundary condition
> in Wien2k. Results for Fe3O4 and Sr3Mn2O7:
>
> Fe3O4, Table for potential value at RMT:
>        Fe1   Fe2   O
> VC     -0.13  0.18  0.37
> VCpois -2.03 -2.08 -1.15
> VCpois(R)=VC(R)+const with great accuracy.
>
> Sr3Mn2O7 with RMT's from setrmt_lapw, Table for potential value at RMT:
>        Sr1   Sr2   Mn    O1    O2    O3
> VC     -472  -382  -231  -258  -230  -250
> VCpois -2.0  -2.0  -2.6  -7.3  -7.5  -7.0
>
> First observation: the values differ by factors 35-235. How is the
> boundary condition for vcoul defined in Wien2k?
>
> Second observation: dVC/dR is <0 and dVCpois/dR is >0 for R in the
> neighborhood of RMT. Indeed, the latter behavior corresponds to a
> muffin-tin with negative charge.
>
> Third observation: VCpois(R) .neq. VC(R)+const. The disagreement is
> significantly great, see 1st Attachment.
>
> When the Fe3O4 calculation is used for LEED, the agreement
> theory-experiment is satisfactory [Surf.Sci. 602(2008)1299]. On the
> other hand, a LEED investigation on Sr3Mn2O7 would respond badly on a
> potential disagreement like the one demonstrated in the 1st Attachment.
> 2nd Attachment is SR3Mn2O7.struct.
>
> VC versus VCpois is a dilemma for Sr3Mn2O7. Is there an expert's input
> to w2web that would make the potentials equal? A discussion would be
> much appreciated.
>
> With best regards,
> John Rundgren, KTH, Stockholm
>
>
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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