Dear Prof. Blaha, I did not look at the forces yet, only started with the bulk truncated bulk. I have been interested in a qualitative result, proper relaxation is time consuming and I have little experience.
The problem is that in slab calculation I see a ladder of bands and a decreased band gap. But what one should see (or what I would prefer to see) is something that resembles projected bulk bands, plus some surface states. I calculated projected bulk bands, and they don't match well with the slab bands. I test grep :MM case.scf to make sure there is AFM phase. At the moment I do "Mn-Te-....-Mn-Te" slab, so both terminations in one slab. Having Te termination on both sides led to similar problem with bands. I did not test Mn termination on both sides yet. Best, Lukasz On Sat, Oct 11, 2025 at 10:00 AM Peter Blaha <[email protected]> wrote: > Mn or Te terminated ??? > Same termination on both sides of the slab ? > I'd guess Mn is less problematic in principle. > > How big are the forces on the surface atoms ??? > This gives you an estimate about your structure. > > Am 11.10.2025 um 09:42 schrieb Lukasz Plucinski: > > Dear Prof. Blaha, Prof. Marks, > > > > Thank you for your quick comments. > > > > I am trying to do the 0001 surface of MnTe (NiAs lattice). > > > > Making partial coverages for relaxation is hard, I don't want to deal > > with folded bands. I did not do any relaxation so far, but I am not sure > > relaxation with 1x1 cell it will solve the problem. > > > > Without DFT+U there is still bulk band gap, and bulk bands change quite > > a lot near VBM, so this not a solution. > > > > I am also thinking of trying H atom on both sides of the slab. > > > > Best, > > Lukasz > > > > On Sat, Oct 11, 2025 at 8:54 AM Peter Blaha <[email protected] > > <mailto:[email protected]>> wrote: > > > > You post 2 questions: > > > > Your calculations of the slab without field do not give expected > > results ?? > > > > Since we do not know any details - hard to comment. How many layers ? > > How much vacuum ? Note: Polar surfaces are always a problem and your > > model has probably 2 inequivalent surfaces, a lot of dangling bonds, > ... > > > > Polar surfaces show usually huge reconstructions / become metallic / > > have in reality stoichiometry changes or H-termination to reach > > neutrality or bond-saturation / ... > > > > A periodic model for them is always a bit problematic due to long > range > > coulomb forces and dipole effects .... > > > > You should be sure your model is realistic and applicable before > using > > an E-field. > > ------------------------------------------ > > What should I use for efield,.... ? > > > > Start with the values in the UG. Note: Efield is in Ry units. You > have > > to consider your unit cell length (actually half of it), and the real > > field is then Efield/c/2. Without screening, this will introduce a > > force of efield/c/2 on the atoms and thus I'd suggest to use an > > efield to get 50-100 mRy/bohr. > > You will see how much of this is screened by the electron density > > redistribution during scf and eventually you can relax the structure > to > > see the change of positions due to the field. For the latter, I'd fix > > the middle of the slab, otherwise the whole slab may translate in the > > field .... > > > > You probably don't have inversion and mirror symmetry, but in case > you > > do, break it manually !!! > > > > Am 10.10.2025 um 20:05 schrieb Lukasz Plucinski: > > > Dear All, > > > > > > I have been trying to calculate a slab of a polar semiconductor. > > > Unfortunately, there seems to be an effect of an electric field > > across > > > the slab. > > > > > > I see that one can add external E field by including line 4 in > > case.in0 > > > file: "IFIELD, EFIELD, WFIELD". I understand that my slab > should be > > > positioned at around 1/4 of the unit cell (so, a lot of vacuum), > to > > > make use of the zig-zag potential. > > > > > > So far I calculated the slab (without E field), and I can see a > > ladder > > > of bands, instead of something resembling the "projected bulk band > > > structure". Is there a way to read some parameters from this > > slab, in > > > order to have an educated guess for the "IFIELD, EFIELD, WFIELD" > > values? > > > > > > Best, > > > Lukasz > > > > > > _______________________________________________ > > > Wien mailing list > > > [email protected] > > <mailto:[email protected]> > > > http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien <http:// > > zeus.theochem.tuwien.ac.at/mailman/listinfo/wien> > > > SEARCH the MAILING-LIST at: http://www.mail-archive.com/ > > [email protected]/index.html <http://www.mail- > > archive.com/[email protected]/index.html> > > > > -- > > > ----------------------------------------------------------------------- > > Peter Blaha, Inst. f. Materials Chemistry, TU Vienna, A-1060 Vienna > > Email: [email protected] <mailto:[email protected]> > > WWW: http://www.imc.tuwien.ac.at <http://www.imc.tuwien.ac.at> > > WIEN2k: http://www.wien2k.at <http://www.wien2k.at> > > > ------------------------------------------------------------------------- > > > > _______________________________________________ > > Wien mailing list > > [email protected] <mailto: > [email protected]> > > http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien <http:// > > zeus.theochem.tuwien.ac.at/mailman/listinfo/wien> > > SEARCH the MAILING-LIST at: http://www.mail-archive.com/ > > [email protected]/index.html <http://www.mail- > > archive.com/[email protected]/index.html> > > > > > > _______________________________________________ > > Wien mailing list > > [email protected] > > http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien > > SEARCH the MAILING-LIST at: > http://www.mail-archive.com/[email protected]/index.html > > -- > ----------------------------------------------------------------------- > Peter Blaha, Inst. f. Materials Chemistry, TU Vienna, A-1060 Vienna > Email: [email protected] > WWW: http://www.imc.tuwien.ac.at WIEN2k: http://www.wien2k.at > ------------------------------------------------------------------------- > > _______________________________________________ > Wien mailing list > [email protected] > http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien > SEARCH the MAILING-LIST at: > http://www.mail-archive.com/[email protected]/index.html >
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