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

[Dr. K. C. Bhamu]

Dear Prof. Marks,
I got the detailed information from my experimental colleague later got to
know that the stoichiometry of my system is WO_(3-x) not WO_3. Having some
Oxygen deficiency on the surface layer stabilized the surface. There are
similar reports available in the literature as well which supports my
calculations.
Thanks for all of your responses.
My reply is just to update the thread so that later it can be useful for
someone who deals similar problem.

Regards
Bhamu




On Fri, Jun 25, 2021 at 11:40 PM Laurence Marks 
wrote:

> Agreed, although to make the bulk truncation valence neutral involves W 5+
> which is unusual. As you say, the O "sticking out" is unreal, as it would
> be 1-. If it moves closer to the W below that becomes 7+ which is silly.
>
> The first thing to do is work out what the actual experimental conditions
> are -- air, UHV, some catalytic gas mix, unknown. Then you can start to
> construct relevant models.It is easy to construct bad models!
>
> N.B., remember that STO/LAO is constrained, and forced to be different if
> there are no O vacancies.
>
> On Fri, Jun 25, 2021 at 9:20 AM Peter Blaha 
> wrote:
>
>> A W atom could have other formal valencies than 6+ and an electronic
>> reconstruction is not impossible (remember the famous LAO/STO interface)
>>
>> Of course the surface depends a lot on the preparation conditions and on
>> the vacuum / O partial pressure, H2O traces (or even "water") ...
>> There could be several possible surface reconstructions. Thus you can
>> try various supercells with W vacancies to reduce the formal 2+ charge)
>> or some O on top (but I don't like this "sticking out").
>> Finally do the thermodynamics and calculate a surface phase diagram as
>> function of O partial pressure.
>>
>> In any case, I hope you have followed what Ludmilla said and use the
>> theoretical lattice parameter (just in case- it could be much larger
>> with PBE than experiment).
>>
>> And clear is: if the surface layer lifts off, it is a clear indication
>> that your model is very "unrealistic".
>>
>> Am 25.06.2021 um 14:43 schrieb Laurence Marks:
>> > 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
>> > http://www.numis.northwestern.edu 
>> >
>> > On Fri, Jun 25, 2021, 07:16 Peter Blaha > > > 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 .
>> >
>> >
>
> --
> Professor Laurence Marks
> Department of Materials Science and Engineering
> Northwestern University
> www.numis.northwestern.edu
> "Research is to see what everybody else has seen, and to think what nobody
> else has thought" Albert Szent-Györgyi
> ___
> Wien mailing list
> Wien@zeus.theochem.tuwien.ac.at
> http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
> SEARCH the MAILING-LIST at:
> http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html
>
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Re: [Wien] Top surface layer seems to be isolated from the rest of the system

[Lyudmila Dobysheva]

25.06.2021 10:29, Dr. K. C. Bhamu wrote:
I am trying to relax the WO3 surface structure (1x1x5 with 15 Ang 
vacuum). 

...
I see after relaxation, the top layer detached from the system (the W-O 
bond length increased from 1.9 to 2.3 Ang)


Maybe just to discuss: imagine that such a structure has minimum at 
larger a and b, so larger volume per atom. And here ab are fixed. Then 
the system tend to increase the volume in the only allowed direction, 
that is c. Look: both 4th and 5th layers move away, that is all 
non-fixed W layers.
I'd try to first relax the lattice parameters ab, let it have the 
desired volume per atom.
And of course you force the system to have geometry of the surface 
unrealistic, this dangling oxygens...


Best wishes
Lyudmila Dobysheva
--
http://ftiudm.ru/content/view/25/103/lang,english/
Institute of Physics and Technology,
Udmurt Federal Research Center, Ural Br. of Rus.Ac.Sci.
426000 Izhevsk Kirov str. 132
Russia
---
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Re: [Wien] Top surface layer seems to be isolated from the rest of the system

[Laurence Marks]

Agreed, although to make the bulk truncation valence neutral involves W 5+
which is unusual. As you say, the O "sticking out" is unreal, as it would
be 1-. If it moves closer to the W below that becomes 7+ which is silly.

The first thing to do is work out what the actual experimental conditions
are -- air, UHV, some catalytic gas mix, unknown. Then you can start to
construct relevant models.It is easy to construct bad models!

N.B., remember that STO/LAO is constrained, and forced to be different if
there are no O vacancies.

On Fri, Jun 25, 2021 at 9:20 AM Peter Blaha 
wrote:

> A W atom could have other formal valencies than 6+ and an electronic
> reconstruction is not impossible (remember the famous LAO/STO interface)
>
> Of course the surface depends a lot on the preparation conditions and on
> the vacuum / O partial pressure, H2O traces (or even "water") ...
> There could be several possible surface reconstructions. Thus you can
> try various supercells with W vacancies to reduce the formal 2+ charge)
> or some O on top (but I don't like this "sticking out").
> Finally do the thermodynamics and calculate a surface phase diagram as
> function of O partial pressure.
>
> In any case, I hope you have followed what Ludmilla said and use the
> theoretical lattice parameter (just in case- it could be much larger
> with PBE than experiment).
>
> And clear is: if the surface layer lifts off, it is a clear indication
> that your model is very "unrealistic".
>
> Am 25.06.2021 um 14:43 schrieb Laurence Marks:
> > 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
> > http://www.numis.northwestern.edu 
> >
> > On Fri, Jun 25, 2021, 07:16 Peter Blaha  > > 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 .
> >
> >

-- 
Professor Laurence Marks
Department of Materials Science and Engineering
Northwestern University
www.numis.northwestern.edu
"Research is to see what everybody else has seen, and to think what nobody
else has thought" Albert Szent-Györgyi
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Re: [Wien] Top surface layer seems to be isolated from the rest of the system

[Peter Blaha]

A W atom could have other formal valencies than 6+ and an electronic 
reconstruction is not impossible (remember the famous LAO/STO interface)


Of course the surface depends a lot on the preparation conditions and on 
the vacuum / O partial pressure, H2O traces (or even "water") ...
There could be several possible surface reconstructions. Thus you can 
try various supercells with W vacancies to reduce the formal 2+ charge) 
or some O on top (but I don't like this "sticking out").
Finally do the thermodynamics and calculate a surface phase diagram as 
function of O partial pressure.


In any case, I hope you have followed what Ludmilla said and use the 
theoretical lattice parameter (just in case- it could be much larger 
with PBE than experiment).


And clear is: if the surface layer lifts off, it is a clear indication 
that your model is very "unrealistic".


Am 25.06.2021 um 14:43 schrieb Laurence Marks:

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 > 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
 > mailto:laurence.ma...@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

>
 >
 >     On Fri, Jun 25, 2021, 01:59 Laurence Marks
mailto:laurence.ma...@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

>
 >
 >         On Fri, Jun 25, 2021, 01:31 Dr. K. C. Bhamu
mailto:kcbham...@gmail.com>
 >         >> wrote:
 >
 >             Dear Wien2k Users,
 >
 >   

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

[Dr. K. C. Bhamu]

Thank you Prof. Peter for your good suggestion.

I have tried with passivating the bottom oxygen atoms that I consider equal
to removing those oxygen atoms.

I tried with 6 layers as well. I don't think more than 6 layers will fix
the problem.

Thank you,
Bhamu

On Fri, Jun 25, 2021, 9:16 PM Peter Blaha 
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
> > mailto:laurence.ma...@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
> > www.numis.northwestern.edu 
> >
> > On Fri, Jun 25, 2021, 01:59 Laurence Marks  > > 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
> > www.numis.northwestern.edu 
> >
> > On Fri, Jun 25, 2021, 01:31 Dr. K. C. Bhamu  > > 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
> >
> >
> >
> >
> >
> > ___
> > Wien mailing list
> > Wien@zeus.theochem.tuwien.ac.at
> > 
> >
> https://urldefense.com/v3/__http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien__;!!Dq0X2DkFhyF93HkjWTBQKhk!Day7KZQBXQaPn8HGxSpldvOiJzObtS73z_8I17izzlA5ZmuvSj27rMzSsjCo-btL6FGi9Q$
> > <
> 

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

[Laurence Marks]

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  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 
> 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
>> > mailto:laurence.ma...@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.ma...@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 <
>> kcbham...@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 

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

[Laurence Marks]

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 
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
> > mailto:laurence.ma...@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  >
> >
> > On Fri, Jun 25, 2021, 01:59 Laurence Marks  > > 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  > > 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
> >
> >
> >
> >
> >
> > 

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

[Peter Blaha]

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 
mailto:laurence.ma...@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
www.numis.northwestern.edu 

On Fri, Jun 25, 2021, 01:59 Laurence Marks mailto:laurence.ma...@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
www.numis.northwestern.edu 

On Fri, Jun 25, 2021, 01:31 Dr. K. C. Bhamu mailto:kcbham...@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

).

I would appreciate it if someone shares their experience
with me.

Regards
Bhamu





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

[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 
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
> www.numis.northwestern.edu
>
> On Fri, Jun 25, 2021, 01:59 Laurence Marks 
> 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
>> www.numis.northwestern.edu
>>
>> On Fri, Jun 25, 2021, 01:31 Dr. K. C. Bhamu  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
>>> 
>>> ).
>>>
>>> I would appreciate it if someone shares their experience with me.
>>>
>>> Regards
>>> Bhamu
>>>
>>>
>>>
>>>
>>>
>>> ___
>>> Wien mailing list
>>> Wien@zeus.theochem.tuwien.ac.at
>>>
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>>>
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Re: [Wien] Top surface layer seems to be isolated from the rest of the system

[Laurence Marks]

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
www.numis.northwestern.edu

On Fri, Jun 25, 2021, 01:59 Laurence Marks  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
> www.numis.northwestern.edu
>
> On Fri, Jun 25, 2021, 01:31 Dr. K. C. Bhamu  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
>> 
>> ).
>>
>> I would appreciate it if someone shares their experience with me.
>>
>> Regards
>> Bhamu
>>
>>
>>
>>
>>
>> ___
>> Wien mailing list
>> Wien@zeus.theochem.tuwien.ac.at
>>
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>>
>
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Re: [Wien] Top surface layer seems to be isolated from the rest of the system

[Laurence Marks]

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
www.numis.northwestern.edu

On Fri, Jun 25, 2021, 01:31 Dr. K. C. Bhamu  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
> 
> ).
>
> I would appreciate it if someone shares their experience with me.
>
> Regards
> Bhamu
>
>
>
>
>
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> Wien mailing list
> Wien@zeus.theochem.tuwien.ac.at
>
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