Dear Thomas, thank you for your detailed reply!
If I understood this correctly, the ideal situation would be to have the slab in the center of the cell Atom xx yy 0.5 (in crystal coordinates) to center the dipole at 0% (=100% due to PBC) a reasonable choice would be emaxpos=0.95 and eopreg=0.10. In the dipole example they located the atoms around z=0 of the cells and put the dipole close to the center of the cell. Muchas Gracias/Vielen Dank from Spain, Christoph On Fri, Apr 27, 2018 at 10:59 AM, Thomas Brumme < thomas.bru...@uni-leipzig.de> wrote: > Dear Chris, > > both planes of the dipole (the one at emaxpos and the one with the > opposite charge at emaxpos+eopreg) have to be in the vacuum region. > In fact, there should be enough space such that the wavefunctions are > essentially zero at the dipole planes. However, if the dipole is too large, > charge can spill into the vacuum region as plane waves are not localized > on the system and the charge could be in a lower energy state at the > dipole. In other words. don't use 50 Angstrom of vacuum as this will lead > to a very low minimum in the total potential at the dipole. > See also this paper: > > https://journals.aps.org/prb/abstract/10.1103/PhysRevB.85.045121 > > In this paper charged systems are discussed but similar things apply to > the dipole correction. Thus, if your system is centered at 50% of the > cell, center the dipole at zero and converge things with increasing the > size along z. > > Regards > > Thomas > > > On 26.04.2018 14:00, Christoph Wolf wrote: > > 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. > > and > > 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! > > Best, > Chris > > > 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 > > > _______________________________________________ > users mailing > listusers@lists.quantum-espresso.orghttps://lists.quantum-espresso.org/mailman/listinfo/users > > > -- > Dr. rer. nat. Thomas Brumme > Wilhelm-Ostwald-Institute for Physical and Theoretical Chemistry > Leipzig University > Phillipp-Rosenthal-Strasse 31 > 04103 Leipzig > > Tel: +49 (0)341 97 36456 > > email: thomas.bru...@uni-leipzig.de > > -- Postdoctoral Researcher Center for Quantum Nanoscience, Institute for Basic Science Ewha Womans University, Seoul, South Korea
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