[Pw_forum] Question about Work Function calculation

[nima nariman]

Dear PWSCF users/developers,

I have started to learn how to calculate work function for modified Ge-surfaces with organic molecules. The WF_example was very helpful but still there is something that I dont understand:

1) How slab potential is calculated in the example and why macroscopic average for the energy E = "17.8087" Ry is taken? ( I thought it's the middle point but its not)
2) Matching macroscopic/planar averages at the borders in the case of modified surfaces needs lots of vacuum. Is the vacuum length the only effective parameter here? How accurate matching should be?
(In my case sometimes for same chains but different lengths I need to give longer vacuum for shorter chain compare to longer one to achieve the matching!!! is it logical? )

I have read all the posts for work function but didn't get my answer. 
Any idea is highly appreciated,

Regards,

Daniel
Electronic Engineering Department, UCC, Ireland 
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