[Wien] Plotting surface potential

[Peter Blaha]

Hi,

The problem you report is most likely NOT due to your fault and unfortunately
it is also present in the scf cycle.

What version of WIEN are you using ?

In LDA the problems should be smaller.

In GGA we have to use various cutoffs (for the density and for the gradients)
and after some tests made by some WIEN-user, those limits were set (now to
fairly small values and I could imagine they are too small). I
could imagine that for very small densities the numerical gradients might be
huge and than such unphysical XC-potential could arise due to not well
chosen cutoffs.

I need to check this in detail. When you are using the latest WIEN2k version,
please send struct and clmsum file to my personal email adress (not the
WIEN-mailing list), otherwise try the latest version.

PS: I checked it and can see that the printing of vcoul does not work anymore.
It seems to happen during parallelization of lapw0. I'll fix this too.

> I have a problem plotting the potential of metal surfaces. When I plot
> it, say for Cu(111) surface, I see a groove like feature parallel to the
> surface located somewhere at the barrier region. The depth of that
> groove is 0.2Ry!!! and the width is about 2 angstroms.   I found that it
> comes from the exchange correlation part of potential that looks totally
> unphysical, because the charge density in that region behaves
> reasonably, namely decays exponentially and is very low. The feature is
> stable with respect to a change in Gmax and/or RKM.  Even if I increase
> Gmax from 14 to 40 and RKM from 7 to 9.5, it remains the same. I cannot
> attach the picture to the message, because the file size is about 600
> kB. If someone is interested in, I can send it to his/her personal address.
>
> First, I would like to understand if this feature is a result of my
> misuse of the lapw5, or some bug in lapw5, or (that would be too bad) it
> appears in SCF calculations. Of course, in case of  the clean Cu surface
> the barrier is high and I guess this feature does not affect the
> occupied states to much, but when I put alkali metal on it, the work
> function is significantly reduced and that feature could give me "very
> very interesting" effects. Could anyone help me to solve this problem?
>
> Another question is about oscillations of potential in the vacuum
> region. They do decrease when I increase Gmax. But what is amusing,
> charge density is very smooth even at smaller values of Gmax and RKM.
>
> Now, let me show you haw I do it.
>
> x lapw0 -p -c  (with R2V in case.in0)
> x lapw5 -c (to create lapw5.def)
> replace case.clmval with case.r2v (or case.vcoul) in lapw5.def
> lapw5 lapw5.def
>
> By the way, I found in the manual, that case.vcoul should comprise of
> both total and Coulomb potentials, but it looks like it contains only
> total one.
>
> Thank you in advance for your suggestions,
>
> Sergey Stolbov
>
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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
Phone: +43-1-58801-15671             FAX: +43-1-58801-15698
Email: blaha at theochem.tuwien.ac.at    WWW: http://info.tuwien.ac.at/theochem/
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