[Wien] Plotting the Coulomb potential

[stolbov]

Dear Wien2k users,

I have some problem when plotting Coulomb potential for a slabs which 
mimic metal surfaces, more specifically Pd(111) and Pd(211) surfaces 
(clean and with adsorbates). I run lapw2 for energies including only 
actual valence states and then lapw5 with corresponding replacement in 
lapw5.def. Everything looks OK, except vacuum region, where I see an 
intensive noise instead of a smooth behavior. This is not periodic 
oscillation, but real noise that suggests that it originates not from 
low RKM cutoff , but from something else. My questions are:
a) Where does it come from?
b) How could I avoid it?

I appreciate your suggestions in advance,

Sergey Stolbov