[Wien] Plotting surface potential

Peter Blaha pblaha at zeus.theochem.tuwien.ac.at
Thu Dec 18 09:21:46 CET 2003


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
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Email: blaha at theochem.tuwien.ac.at    WWW: http://info.tuwien.ac.at/theochem/
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