[Pw_forum] Workfunction from slab calculations?

[Georg Heimel]

Hi everyone,

Having tried to extract the workfunction from slab calculation performed
with PWscf i ran into some unexpected troubles. In principle, the simple
version should go like this:

- perform slab calculations
- get fermi energy from output
- plot plane-averaged full electrostatic potential (v_ion+v_hartree+v_c)
- get value of potential in the middle of the vacuum region
- subtract fermi energy from that
- done

doing this with pwscf (specifying plot_num=1 in the pp.x input file and
using average.x thereafter) yields systematically wrong numbers.

What can one do? Seeing that the eigenvalues and fermi energy can be
positive and that the values sclae with the inverse of the unit cell volume,
i guess that some constants have been dropped in PWscf  (like v_c(G=0) or
the "alpha"-term from the pseudopotentials).

Is there any straightforward way to extract the right numbers?

many thanks!

PS: by the way: what units is the electrostatic potential given in? It
does'nt say anywhere.

Georg


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DI Dr. Georg Heimel
School of Chemistry & Biochemistry
Georgia Institute of Technology
Atlanta, GA 30332-0400
USA
Phone: ++1/404/894 6456
Fax:   ++1/404/894 7452
EMail: georg.heimel at chemistry.gatech.edu
Web:   http://www.muckisnspirit.com
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