<div dir="auto">You should look at the BVS, i.e. "grep Bond *tnn" and compare it to what you have for bulk. You will see that you surface has bad values, so will be unstable. You need to do a lot more thinking and analysis (weeks) to find a chemically reasonable surface.<br><br><div data-smartmail="gmail_signature">---<br>Professor Laurence Marks (Laurie)<br>Department of Materials Science and Engineering<br>Northwestern University<br><a href="http://www.numis.northwestern.edu">www.numis.northwestern.edu</a><br>"Research is to see what everybody else has seen, and to think what nobody else has thought" Albert Szent-Györgyi</div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Mon, Jul 24, 2023, 05:28 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:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Yes, R cells are first converted into H (making it already 3 times <br>
larger than the primitive R cell).<br>
<br>
The "accepting repeat atoms at z=0" makes the non-stoichiometry. It <br>
leads to 2 identical surfaces and inversion symmetry (cheaper calc), but <br>
non-stoiciometry.<br>
It is not always clear what the best model for a surface is. Yours is Te <br>
terminated, but maybe another termination is more favorable (Bi, or <br>
maybe another Te-layer ?)<br>
<br>
Am 24.07.2023 um 10:51 schrieb Burhan Ahmed:<br>
> The 6ql slab is created with 1x1x2 supercell with vacuum in Z direction <br>
> and accepting repeat atoms at z=0 (using x supercell program). At first <br>
> the x supercell convert rhombohedral cell into hexagonal and then from <br>
> hexagonal cell I have created the 1x1x2 supercell and then I took the <br>
> structure suggested by sgroup.<br>
> <br>
> Yes sorry for that I have used MSR1a method for the relaxation.<br>
> <br>
> The force convergence is set to 1 Ry.<br>
> <br>
> On Mon, 24 Jul, 2023, 2:06 pm Peter Blaha, <<a href="mailto:peter.blaha@tuwien.ac.at" target="_blank" rel="noreferrer">peter.blaha@tuwien.ac.at</a> <br>
> <mailto:<a href="mailto:peter.blaha@tuwien.ac.at" target="_blank" rel="noreferrer">peter.blaha@tuwien.ac.at</a>>> wrote:<br>
> <br>
> I'm not sure how you get a non-stoichimetric cell with a multiplicative<br>
> number of unit cells, unless you said you want to repeat the atom at<br>
> z=0.<br>
> Of course, without this extra layer, you may not have inversion and get<br>
> 2 different surface terminations in one calculation. This is the usual<br>
> problem of slabs.<br>
> Also symmetry will be reduced and "multiplicity" errors occur. But<br>
> both,<br>
> nn and sgroup create new struct files where this has been corrected.<br>
> <br>
> If possible, I would also go to a smaller number of layers.<br>
> <br>
> <br>
> Am 24.07.2023 um 10:13 schrieb Burhan Ahmed:<br>
> > That is very true. I made the slab using the tutorial available<br>
> in the<br>
> > wien2k user manual by executing x-supercell program. What I found is<br>
> > that the 6ql supercell consist of an extra Te atom. But whenever<br>
> I try<br>
> > to remove this atom I got multiplicity error. Sir, what is best<br>
> possible<br>
> > way of making slab with vacuum or surfaces??<br>
> ><br>
> > Thanks<br>
> ><br>
> > Regards<br>
> ><br>
> > Burhan Ahmed<br>
> ><br>
> > *Research Scholar, AUS *<br>
> ><br>
> > *From: *Laurence Marks <mailto:<a href="mailto:laurence.marks@gmail.com" target="_blank" rel="noreferrer">laurence.marks@gmail.com</a><br>
> <mailto:<a href="mailto:laurence.marks@gmail.com" target="_blank" rel="noreferrer">laurence.marks@gmail.com</a>>><br>
> > *Sent: *Saturday, July 22, 2023 6:30 PM<br>
> > *To: *A Mailing list for WIEN2k users<br>
> > <mailto:<a href="mailto:wien@zeus.theochem.tuwien.ac.at" target="_blank" rel="noreferrer">wien@zeus.theochem.tuwien.ac.at</a><br>
> <mailto:<a href="mailto:wien@zeus.theochem.tuwien.ac.at" target="_blank" rel="noreferrer">wien@zeus.theochem.tuwien.ac.at</a>>><br>
> > *Subject: *Re: [Wien] calculation with lmbj potential<br>
> ><br>
> > Others will probably give you suggestions about converging mBJ. Some<br>
> > deeper comments.<br>
> ><br>
> > The most common reason that calculations behave badly is user error.<br>
> > Sometimes this is doing the initialization wrong, often it is<br>
> creating<br>
> > an inappropriate model. Just because one can use x supercell or<br>
> related<br>
> > codes to create atomic positions does /not/ make them sensible.<br>
> ><br>
> > Your slab has a composition Bi12 Te19, i.e. it is Te rich. You<br>
> therefore<br>
> > have a reduced, n-type semiconductor with a small gap (about 0.1eV)<br>
> > which will behave badly. If you look at your BVS you will see<br>
> that atom<br>
> > Te7 is severely underco-ordinated (unstable).<br>
> ><br>
> > I doubt that your slab will ever converge to anything which<br>
> should be<br>
> > published. Surfaces are not simple, it is unfortunately too easy<br>
> to set<br>
> > something up and get it wrong. (There are many papers in the<br>
> literature<br>
> > of dubious merit.)<br>
> ><br>
> > On Fri, Jul 21, 2023 at 10:47 PM Burhan Ahmed<br>
> <<a href="mailto:burhan.ahmed@aus.ac.in" target="_blank" rel="noreferrer">burhan.ahmed@aus.ac.in</a> <mailto:<a href="mailto:burhan.ahmed@aus.ac.in" target="_blank" rel="noreferrer">burhan.ahmed@aus.ac.in</a>><br>
> > <mailto:<a href="mailto:burhan.ahmed@aus.ac.in" target="_blank" rel="noreferrer">burhan.ahmed@aus.ac.in</a> <mailto:<a href="mailto:burhan.ahmed@aus.ac.in" target="_blank" rel="noreferrer">burhan.ahmed@aus.ac.in</a>>>><br>
> wrote:<br>
> ><br>
> > Dear experts, I am doing an scf calculation taking lmbj<br>
> potential.<br>
> > My system is a slab of 6ql with a vacuum of 40 ang along c-axix.<br>
> > Whenever I try to run the scf calculation including SOC,<br>
> after 999<br>
> > iteration the scf is still not converged. I have analyzed the scf<br>
> > file, it shows the fluctuating nature. At first the selected<br>
> Rmt was<br>
> > 2.5 then I reduces it to 2.34 and again convergence failed<br>
> after 999<br>
> > cycle. I have included -hdlo and -lvns 8 switch in init_lapw<br>
> as it<br>
> > shows heavy atom. I am attaching the case.struct file. Hoping for<br>
> > any suggestion/solution.<br>
> ><br>
> > Regards<br>
> ><br>
> > Burhan Ahmed<br>
> ><br>
> > *Research Scholar, AUS *<br>
> ><br>
> > _______________________________________________<br>
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> <a href="http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html" rel="noreferrer noreferrer" target="_blank">http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html</a> <<a href="http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html" rel="noreferrer noreferrer" target="_blank">http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html</a>> <<a href="http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html" rel="noreferrer noreferrer" target="_blank">http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html</a> <<a href="http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html" rel="noreferrer noreferrer" target="_blank">http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html</a>>><br>
> ><br>
> ><br>
> > --<br>
> ><br>
> > Professor Laurence Marks (Laurie)<br>
> > Department of Materials Science and Engineering<br>
> > Northwestern University<br>
> > <a href="http://www.numis.northwestern.edu" rel="noreferrer noreferrer" target="_blank">www.numis.northwestern.edu</a> <<a href="http://www.numis.northwestern.edu" rel="noreferrer noreferrer" target="_blank">http://www.numis.northwestern.edu</a>><br>
> <<a href="http://www.numis.northwestern.edu" rel="noreferrer noreferrer" target="_blank">http://www.numis.northwestern.edu</a> <<a href="http://www.numis.northwestern.edu" rel="noreferrer noreferrer" target="_blank">http://www.numis.northwestern.edu</a>>><br>
> > "Research is to see what everybody else has seen, and to think what<br>
> > nobody else has thought", Albert Szent-Györgyi<br>
> ><br>
> ><br>
> > _______________________________________________<br>
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> <br>
> -- <br>
> --------------------------------------------------------------------------<br>
> Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna<br>
> Phone: +43-1-58801-165300<br>
> Email: <a href="mailto:peter.blaha@tuwien.ac.at" target="_blank" rel="noreferrer">peter.blaha@tuwien.ac.at</a> <mailto:<a href="mailto:peter.blaha@tuwien.ac.at" target="_blank" rel="noreferrer">peter.blaha@tuwien.ac.at</a>> <br>
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-- <br>
--------------------------------------------------------------------------<br>
Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna<br>
Phone: +43-1-58801-165300<br>
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</blockquote></div>