[Wien] Top surface layer seems to be isolated from the rest of the system

Fri Jun 25 15:06:04 CEST 2021

N.B., b) Does not work without massive rearrangements. A dangling "O" on
top is unchemical.

There are many ways to construct wrong models!

_____
Professor Laurence Marks
"Research is to see what everybody else has seen, and to think what nobody
else has thought", Albert Szent-Györgyi
www.numis.northwestern.edu

On Fri, Jun 25, 2021, 07:43 Laurence Marks <laurence.marks at gmail.com> wrote:

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