[Wien] Plotting surface potential

[stolbov]

Dear Wien users,

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