<div dir="ltr">Dear Prof. Blaha, Prof. Marks,<div><br></div><div>Thank you for your quick comments.<br><div><br></div><div>I am trying to do the 0001 surface of MnTe (NiAs lattice).</div><div><br></div><div>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.</div><div><br></div><div>Without DFT+U there is still bulk band gap, and bulk bands change quite a lot near VBM, so this not a solution.</div></div><div><br></div><div>I am also thinking of trying H atom on both sides of the slab.</div><div><br></div><div>Best,</div><div>Lukasz</div></div><br><div class="gmail_quote gmail_quote_container"><div dir="ltr" class="gmail_attr">On Sat, Oct 11, 2025 at 8:54 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">You post 2 questions:<br>
<br>
Your calculations of the slab without field do not give expected 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 across <br>
> the slab.<br>
> <br>
> I see that one can add external E field by including line 4 in 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 ladder <br>
> of bands, instead of something resembling the "projected bulk band <br>
> structure". Is there a way to read some parameters from this slab, in <br>
> order to have an educated guess for the "IFIELD, EFIELD, WFIELD" values?<br>
> <br>
> Best,<br>
> Lukasz<br>
> <br>
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-- <br>
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Peter Blaha, Inst. f. Materials Chemistry, TU Vienna, A-1060 Vienna<br>
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