open shell molecule NO

Questions and doubts about the spin-dependent version of Yambo.

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open shell molecule NO

Postby vitoversace » Tue Jul 08, 2014 7:51 pm

Dear Daniele,

i would like to run a gw+bse calculation on open shell molecule NO, but i get absolutely non sense result for the absorption spectrum.
I don't know why but this is maybe due to metallic system which i have now.
Attached is my input file. Please have a look on it

Best greetings
Vito
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Re: open shell molecule NO

Postby Daniele Varsano » Tue Jul 08, 2014 9:41 pm

Dear Vito,
yes, the strange behavior at low energy is due to the metallic character. You can check your ground state if it is meaningful. It looks strange to me that you find a fractional occupation on both spin channels. I'm not expert on that, probably people more expert on spin resolved calculation can help you.
Best,
Daniele
Dr. Daniele Varsano
S3-CNR Institute of Nanoscience and MaX Center, Italy
MaX - Materials design at the Exascale
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Re: open shell molecule NO

Postby Davide Sangalli » Tue Jul 08, 2014 11:33 pm

Dear Vito,
the electronic temperature of yout system is very high.
** Electronic Temp. [ev K]: 0.2721 3158. **

Yambo by defult converts it from your pwscf grund state calculation.
To change it try to create the setup input file running
"yambo -i -V gen -F 00init.in"
and then set
ElecTemp= 0.000 eV # Electronic Temperature

or some other reasonable value (i.e. 300 K).

Run the setup again
yambo -F 00init.in

After that your results should be more reasonalble.

Davide
Davide Sangalli, PhD
CNR-ISM, Division of Ultrafast Processes in Materials (FLASHit) and MaX Centre
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Re: open shell molecule NO

Postby vitoversace » Wed Jul 09, 2014 1:04 am

Dear Davide,

I did your instructions, now in my r_setup temperature is 0 kelvin, so this is fine.
But YAMBO still considers my system as a metallic system, even if as you see in the attached r_setup i have no metallic states for both spin channels !
I just get the same results as before.

Is my Espresso input for spin resolved calculation correct ?
How can i set the temperature in Espresso to 0 K ???

Bests
Vito
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Re: open shell molecule NO

Postby Davide Sangalli » Wed Jul 09, 2014 7:04 pm

Dear Vito,
I'm not sure there is something wrong.
NO seems to be a peculiar system. Are you sure these are not the correct results .... ?

Davide
Davide Sangalli, PhD
CNR-ISM, Division of Ultrafast Processes in Materials (FLASHit) and MaX Centre
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Re: open shell molecule NO

Postby vitoversace » Wed Jul 09, 2014 7:43 pm

Dear Davide,

I just wanted to test BSE for an open shell molecule like NO which has its first excitation energy at 5.7 eV.
But it is not about NO only, generally for any given open shell molecule or solid in spin polarized calculations,
Espresso generates metallic states which cause trouble. YAMBO gives a warning "the system is metallic", too.
As you know BSE is of no use for metallic systems.

It is not about getting bad results, it is about getting non-sense results due to this metallic behavior i guess !

Any way have you ever run BSE on any open shell molecule AND open shell solid using espresso + yambo ?
I just wanna see one or two examples of it.


Bests
Vito
Vito Versace
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Re: open shell molecule NO

Postby Davide Sangalli » Wed Jul 09, 2014 8:16 pm

Dear Vito,
it is not true that "any given open shell molecule or solid in spin polarized calculations, Espresso generates metallic states which cause trouble".
There are polarized/magnetic system/molecules with a Gap.

However, according to your results, NO seems peculiar. It has two degenerate states at the "Fermi level" with just one electron. I do not know the system.
I guess you would obtain a gap removing one electron from the system (or also adding one). This is likely why NO is "very active".

But I've no idea of how is NO experimentally. Maybe it is a problem of the LDA approximation, or maybe there are other things.
I tryed a quick look on google and this is what I found: http://cgmp.blauplanet.com/adv/nomol.html
It seems cosistent with your result.

In any case you cannot pretend to run the code and get meaningful results without thinking and studying the literature.
It is a wasting of time, ours and yours.

Best,
Davide
Davide Sangalli, PhD
CNR-ISM, Division of Ultrafast Processes in Materials (FLASHit) and MaX Centre
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Re: open shell molecule NO

Postby Daniele Varsano » Wed Jul 09, 2014 8:21 pm

Dear Vito,
if you want to set a lower electronic temperature in quantum espresso, you need to play with the smearing and the degauss value. Of course if you reduce it too much there is a risk of not reaching convergence when you have homo and lumo degenerate.
As you know BSE is of no use for metallic systems.

Anyway I do not fully agree with this statement.

Best,
Daniele
Dr. Daniele Varsano
S3-CNR Institute of Nanoscience and MaX Center, Italy
MaX - Materials design at the Exascale
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