[Wien] Plotting surface potential

[stolbov]

Dear Dr. Blaha,

Thank you very much for your reply. I have recalculated Cu(111) surface 
with LDA and also with PBE96. LDA gives just perfect behavior for XC 
potential around the surface. It is also very smooth in the vacuum 
region. Now it is clear that the noise in vacuum which I talked about 
comes from the error in GGA. PBE96 looks better than PW91, but it has 
some jump where Vxc reaches 0. I have to note that GGA oscillates even 
inside the slab. I attach to the message a one-dimensional plotting 
which shows the Vxc along a certain line normal to the surface for these 
three approximations.

I use the version uploaded and installed in early September 2003. I 
don't know if it is new. The case.clmsum files takes 5.3MB, so I decided 
to send it to you, if you let me know that the version I use is new. 
Thanks again,

Sergey Stolbov

Peter Blaha wrote:

>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
>>
>>_______________________________________________
>>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: +43-1-58801-15671             FAX: +43-1-58801-15698
>Email: blaha at theochem.tuwien.ac.at    WWW: http://info.tuwien.ac.at/theochem/
>--------------------------------------------------------------------------
>
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>  
>

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