<div dir="auto">Sorry Peter, that is also wrong.<div dir="auto"><br></div><div dir="auto">The valence of a WO2 layer is 2+ ; of the O layer 2-. A valence neutral surface comes from</div><div dir="auto">a) Adding OH above every W -- 1-</div><div dir="auto">b) Add 1/2 the O above, and letting the structure relax in a 2x1 cell (or larger) -- the last layer has a valence of 1- per 1x1</div><div dir="auto">c) Adjusting a top WO2 layer so it has a valence of 1+ per 1x1 (tricky)</div><div dir="auto"><br></div><div dir="auto">Note: a) is for wet samples (in air); b) more common for dry but only if the top O can adequately bond; c) less common but not impossible. There is some literature, but I expect many of the existing calculations are dodgy.</div><div dir="auto"><br></div><div dir="auto"><div data-smartmail="gmail_signature" dir="auto">_____<br>Professor Laurence Marks<br>"Research is to see what everybody else has seen, and to think what nobody else has thought", Albert Szent-Györgyi<br><a href="http://www.numis.northwestern.edu">www.numis.northwestern.edu</a></div></div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Fri, Jun 25, 2021, 07:16 Peter Blaha <<a href="mailto:pblaha@theochem.tuwien.ac.at">pblaha@theochem.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">Remove the O atoms, which are sticking out of the lower surface.<br>
This makes the system inversion symmetric and more realistic.<br>
Since you are now not stoichiometric anymore, eventually test with more <br>
than 5 layers .<br>
<br>
Am 25.06.2021 um 13:42 schrieb Dr. K. C. Bhamu:<br>
> Dear Prof. L. Marks,<br>
> Thanks for your suggestions. Yes, WO3 is an insulator.<br>
> <br>
> I am facing the same issue for WC (SG: 187).<br>
> <br>
> I have worked on Ni(OH)2 and ZnO surfaces and I did not face any <br>
> difficulties there. Ni(OH) surface is also polar.<br>
> <br>
> For the present case, I do not have much choice. I was asked to provide <br>
> the absorbance of some molecules on the (100) surface of WO3. The <br>
> experimental group is not using any substrate/support for it.<br>
> <br>
> I will read up on oxide surfaces.<br>
> <br>
> Thank you very much,<br>
> Bhamu<br>
> <br>
> <br>
> <br>
> <br>
> <br>
> <br>
> <br>
> <br>
> On Fri, Jun 25, 2021 at 12:46 PM Laurence Marks <br>
> <<a href="mailto:laurence.marks@gmail.com" target="_blank" rel="noreferrer">laurence.marks@gmail.com</a> <mailto:<a href="mailto:laurence.marks@gmail.com" target="_blank" rel="noreferrer">laurence.marks@gmail.com</a>>> wrote:<br>
> <br>
> N.B., your cell is polar, and you are not satisfying valence<br>
> neutrality or Pauling's rules. It will never occur in reality, and<br>
> any results you obtain with it will move science backwards.<br>
> <br>
> Read up on oxide surfaces, much is known.<br>
> <br>
> _____<br>
> Professor Laurence Marks<br>
> "Research is to see what everybody else has seen, and to think what<br>
> nobody else has thought", Albert Szent-Györgyi<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>
> <br>
> On Fri, Jun 25, 2021, 01:59 Laurence Marks <<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>>> wrote:<br>
> <br>
> Did you check:<br>
> a) The BVS, to ensure that you do not have a GIGO surface?<br>
> b) Whether the system has a decent gap or not -- I believe WO3<br>
> should be an insulator.<br>
> c) Whether you are satisfying valence neutrality at the surface.<br>
> <br>
> I expect you have a GIGO surface, 99.99% probability. You cannot<br>
> just create an oxide supercell and expect it to lead to a<br>
> realistic surface. Fixing layers won't help, and is flawed thinking.<br>
> <br>
> GIGO.<br>
> <br>
> _____<br>
> Professor Laurence Marks<br>
> "Research is to see what everybody else has seen, and to think<br>
> what nobody else has thought", Albert Szent-Györgyi<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>
> <br>
> On Fri, Jun 25, 2021, 01:31 Dr. K. C. Bhamu <<a href="mailto:kcbhamu85@gmail.com" target="_blank" rel="noreferrer">kcbhamu85@gmail.com</a><br>
> <mailto:<a href="mailto:kcbhamu85@gmail.com" target="_blank" rel="noreferrer">kcbhamu85@gmail.com</a>>> wrote:<br>
> <br>
> Dear Wien2k Users,<br>
> <br>
> I am trying to relax the WO3 surface structure (1x1x5 with<br>
> 15 Ang vacuum). The bulk structure crystallizes in 221 SG.<br>
> Then I created the 1x1x5 layered structure and relaxed the<br>
> top two layers with the bottom three layers kept fixed.<br>
> I see after relaxation, the top layer detached from the<br>
> system (the W-O bond length increased from 1.9 to 2.3 Ang),<br>
> you can see from the PDF provided with this email.<br>
> I have tried with QE as well and the same problem I faced there.<br>
> I am wondering if someone has faced a similar experience and<br>
> would like to share his/her experience with me to tackle<br>
> this issue.<br>
> <br>
> I have used a different strategy: with U, with U, with<br>
> dipole correction, without dipole correction, vacuum up<br>
> to 30Ang.<br>
> <br>
> As the bulk system is a high symmetry system, is it the<br>
> reason due to the symmetry? If so then how one can handle it?<br>
> <br>
> I am providing the required information here in the tar<br>
> file (PLEASE DOWNLOAD FROM HERE<br>
> <<a href="https://urldefense.com/v3/__https://we.tl/t-0vedkrUS54__;!!Dq0X2DkFhyF93HkjWTBQKhk!Day7KZQBXQaPn8HGxSpldvOiJzObtS73z_8I17izzlA5ZmuvSj27rMzSsjCo-bt6MCzNAQ$" rel="noreferrer noreferrer" target="_blank">https://urldefense.com/v3/__https://we.tl/t-0vedkrUS54__;!!Dq0X2DkFhyF93HkjWTBQKhk!Day7KZQBXQaPn8HGxSpldvOiJzObtS73z_8I17izzlA5ZmuvSj27rMzSsjCo-bt6MCzNAQ$</a>>).<br>
> <br>
> I would appreciate it if someone shares their experience<br>
> with me.<br>
> <br>
> Regards<br>
> Bhamu<br>
> <br>
> <br>
> <br>
> <br>
> <br>
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-- <br>
--------------------------------------------------------------------------<br>
Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna<br>
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