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
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
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
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
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
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
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
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
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
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
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
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