<div dir="ltr">Dear Prof. Blaha,<br><br>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.<br><br>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.<br><br>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.<br><br>Best,<div>Lukasz</div></div><br><div class="gmail_quote gmail_quote_container"><div dir="ltr" class="gmail_attr">On Sat, Oct 11, 2025 at 10:00 AM Peter Blaha <<a href="mailto:peter.blaha@tuwien.ac.at">peter.blaha@tuwien.ac.at</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">Mn or Te terminated ???<br>
Same termination on both sides of the slab ?<br>
I'd guess Mn is less problematic in principle.<br>
<br>
How big are the forces on the surface atoms ???<br>
This gives you an estimate about your structure.<br>
<br>
Am 11.10.2025 um 09:42 schrieb Lukasz Plucinski:<br>
> Dear Prof. Blaha, Prof. Marks,<br>
> <br>
> Thank you for your quick comments.<br>
> <br>
> I am trying to do the 0001 surface of MnTe (NiAs lattice).<br>
> <br>
> Making partial coverages for relaxation is hard, I don't want to deal <br>
> with folded bands. I did not do any relaxation so far, but I am not sure <br>
> relaxation with 1x1 cell it will solve the problem.<br>
> <br>
> Without DFT+U there is still bulk band gap, and bulk bands change quite <br>
> a lot near VBM, so this not a solution.<br>
> <br>
> I am also thinking of trying H atom on both sides of the slab.<br>
> <br>
> Best,<br>
> Lukasz<br>
> <br>
> On Sat, Oct 11, 2025 at 8:54 AM Peter Blaha <<a href="mailto:peter.blaha@tuwien.ac.at" target="_blank">peter.blaha@tuwien.ac.at</a> <br>
> <mailto:<a href="mailto:peter.blaha@tuwien.ac.at" target="_blank">peter.blaha@tuwien.ac.at</a>>> wrote:<br>
> <br>
> You post 2 questions:<br>
> <br>
> Your calculations of the slab without field do not give expected<br>
> results ??<br>
> <br>
> Since we do not know any details - hard to comment. How many layers ?<br>
> How much vacuum ? Note: Polar surfaces are always a problem and your<br>
> model has probably 2 inequivalent surfaces, a lot of dangling bonds, ...<br>
> <br>
> Polar surfaces show usually huge reconstructions / become metallic /<br>
> have in reality stoichiometry changes or H-termination to reach<br>
> neutrality or bond-saturation / ...<br>
> <br>
> A periodic model for them is always a bit problematic due to long range<br>
> coulomb forces and dipole effects ....<br>
> <br>
> You should be sure your model is realistic and applicable before using<br>
> an E-field.<br>
> ------------------------------------------<br>
> What should I use for efield,.... ?<br>
> <br>
> Start with the values in the UG. Note: Efield is in Ry units. You have<br>
> to consider your unit cell length (actually half of it), and the real<br>
> field is then Efield/c/2. Without screening, this will introduce a<br>
> force of efield/c/2 on the atoms and thus I'd suggest to use an<br>
> efield to get 50-100 mRy/bohr.<br>
> You will see how much of this is screened by the electron density<br>
> redistribution during scf and eventually you can relax the structure to<br>
> see the change of positions due to the field. For the latter, I'd fix<br>
> the middle of the slab, otherwise the whole slab may translate in the<br>
> field ....<br>
> <br>
> You probably don't have inversion and mirror symmetry, but in case you<br>
> do, break it manually !!!<br>
> <br>
> Am 10.10.2025 um 20:05 schrieb Lukasz Plucinski:<br>
> > Dear All,<br>
> ><br>
> > I have been trying to calculate a slab of a polar semiconductor.<br>
> > Unfortunately, there seems to be an effect of an electric field<br>
> across<br>
> > the slab.<br>
> ><br>
> > I see that one can add external E field by including line 4 in<br>
> case.in0<br>
> > file: "IFIELD, EFIELD, WFIELD". I understand that my slab should be<br>
> > positioned at around 1/4 of the unit cell (so, a lot of vacuum), to<br>
> > make use of the zig-zag potential.<br>
> ><br>
> > So far I calculated the slab (without E field), and I can see a<br>
> ladder<br>
> > of bands, instead of something resembling the "projected bulk band<br>
> > structure". Is there a way to read some parameters from this<br>
> slab, in<br>
> > order to have an educated guess for the "IFIELD, EFIELD, WFIELD"<br>
> values?<br>
> ><br>
> > Best,<br>
> > Lukasz<br>
> ><br>
> > _______________________________________________<br>
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