[Wien] Top surface layer seems to be isolated from the rest of the system
Laurence Marks
laurence.marks at gmail.com
Fri Jun 25 14:43:17 CEST 2021
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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