[QE-users] Dipole corrections (dipfield) and the position of the slab

Christoph Wolf wolf.christoph at qns.science
Thu Apr 26 14:00:36 CEST 2018

Dear all,

After trying for a few days I am still a bit puzzled by the "proper
application" of the dipole correction. To test this I have made a sheet of
graphene added hydrogen below and fluorine above. I then apply the
following corrections:

    tefield = .true.
    dipfield =.true.


  eamp        = 0.00
  edir        = 3
  emaxpos     = 0.80 !(=16 Angstrom)
  eopreg      = 0.10 ! (=2 Angstrom)

The cell is 20 A in total. As I shift the layer from 0% of the cell to 50%
cell (whilst keeping above emaxpos at 80% and eopreg at 10% of the cell)
the Fermi level shifts slightly (~0.2-0.5 eV difference) and the
electrostatic potential (pp.x plot num 11 and then planar average using
average.x as in the work-function example) is only "flat" in the vacuum
region when the sample is about 3A from the bottom of the cell (i.e. the z
coordinate of atoms has to be larger than 3 A).

Reading the pw.x input I was under the impression that only emaxpos has to
fall into the vacuum but is there also a "rule of thumb" for eopreg?

Thanks in advance for your help!


PS: I saw the related discussion, but it does not really answer this I
think... http://qe-forge.org/pipermail/pw_forum/2009-December/089951.html
Postdoctoral Researcher
Center for Quantum Nanoscience, Institute for Basic Science
Ewha Womans University, Seoul, South Korea
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