[Pw_forum] Oscillations in macroscopic average of VH+Vbare

[Izaak Williamson]

Dear all,


I am trying to calculate the work function for Cu(100) surface with and without 
bulk reference. The equations used are as follows:

work function w/o bulkref  -->  wf1 = Vvac - EF,slab 
work function with bulkref  -->  wf2 = Vvac - Vslab,int + Vbulk,macro - EF,bulk

The problem is that the macroscopic average of VH+Vbare for the slab is 
oscillating as a function of z (see 05.png). I do not understand why the 
macroscopic average is oscillating. We want to see the convergence of the work 
function with the number of atomic layers in the slab. Due to the oscillation in 
macroscopic average,  the work function dramatically changes when we go from 5 
to 6 layers (4.86641 eV to 3.62728 eV, respectively). This makes it hard to see 
the convergence of wf with number of layers.

Would it be correct to use the average of the macroscopic average of the peaks 
and troughs in calculating wf2? Even if we calculate the average of upper 
oscillations (05.png), I don't know what to do with the trough that comes up 
just before the vacuum region? 

 
Thank you for any help.

-- 
Izaak Williamson
Research Assistant
Physics Department
Boise State University
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