How to get the open shell singlet state (singlet biradical) of ozone (O3)

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I want to get the open shell singlet state of O3 using DFT method but failed. I have searched the internet and got some answer like:
For example, you could generate vectors
with a UHF triplet calculation and read these in to the DFT singlet
calculation with 'odft' enabled and it should strongly bias towards a
symmetry-broken UKS singlet wavefunction

I followed the example. First, I got the triplet vectors. Second I read the triplet vectors and use "odft" and "mult 1". However in the end the wavefunction still come back to the close shell singlet and <S2> = 0.0000.
By using Gaussian package, I can get the open shell state of O3 by using "guess=mix". The open shell state is 0.003a.u. lower in energy than the close shell singlet and <S2>=0.414265.
Is there some method similar to do this?

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Yes, you could do something similar to this. I don't know what the level of mixing is, but what you can do is the following:

Before your second dft task (where you want to compute the open-shell singlet), add to the input deck:

   set mixang 30

You can play with the value to get the state you want.

Also, you may want to look at setting max_ovl in the dft input block to maximize the overlap.

Bert


Quote: Dec 27th 6:09 am
I want to get the open shell singlet state of O3 using DFT method but failed. I have searched the internet and got some answer like:
For example, you could generate vectors
with a UHF triplet calculation and read these in to the DFT singlet
calculation with 'odft' enabled and it should strongly bias towards a
symmetry-broken UKS singlet wavefunction

I followed the example. First, I got the triplet vectors. Second I read the triplet vectors and use "odft" and "mult 1". However in the end the wavefunction still come back to the close shell singlet and <S2> = 0.0000.
By using Gaussian package, I can get the open shell state of O3 by using "guess=mix". The open shell state is 0.003a.u. lower in energy than the close shell singlet and <S2>=0.414265.
Is there some method similar to do this?

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title "oss_read_hf_mixang_2"
SCRATCH_DIR /state/partition1/
memory 3000 mb
geometry noautoz nocenter
symmetry c1
O 0.00000000 0.00000000 -0.50788777
O 0.00000000 -1.07796685 0.25394388
O -0.00000000 1.07796685 0.25394388
end
basis
* library 6-31G**
end
dft
xc b3lyp
ADAPT off
convergence nolevelshifting
odft
mult 1
grid nodisk
max_ovl
end
set mixang 30
task dft

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Dear Bert,
I have tried "set mixang 30" to "set mixang 100", but failed to get the open shell singlet state of O3.
I also tried to combine "set mixang 30" with reading vectors from triplet, but still failed. The final result always leads to the close shell singlet state.
I have put in the input information of mine above.
Have you tried ozone before and successful? If you were successful, can you paste your input file for me?
Thanks a lot!

  • Bert Forum:Admin, Forum:Mod, NWChemDeveloper, bureaucrat, sysop
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Hmmm, weird state. Can you post or send me or post the specific alpha and beta orbitals so I can understand the character you're trying to get to and understand what needs to be done. With a 0.4 S2, wonder if this a spin-contamination and the state is artificially low.

Also, you are not using symmetry in your Gaussian run either?

Bert

Quote: Dec 30th 10:52 am
Dear Bert,
I have tried "set mixang 30" to "set mixang 100", but failed to get the open shell singlet state of O3.
I also tried to combine "set mixang 30" with reading vectors from triplet, but still failed. The final result always leads to the close shell singlet state.
I have put in the input information of mine above.
Have you tried ozone before and successful? If you were successful, can you paste your input file for me?
Thanks a lot!

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Dear Bert,
There is a link on how to calculate the open shell singlet state of ozone using Gaussian.
http://www.cup.uni-muenchen.de/ch/compchem/energy/stability.html
I just followed the procedure of website.
And I think the symmetry is in the Gaussian calculation.
Thanks and regards

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I'm interested in your results, so I know what state you are looking at. Can you send me a copy out your Gaussian output with the HOMO and LUMO for both the alpha and beta orbitals of this biradical?

And, can you double check if you are using point group symmetry, and which point group.

Thanks,

Bert


Quote: Jan 5th 6:44 am
Dear Bert,
There is a link on how to calculate the open shell singlet state of ozone using Gaussian.
http://www.cup.uni-muenchen.de/ch/compchem/energy/stability.html
I just followed the procedure of website.
And I think the symmetry is in the Gaussian calculation.
Thanks and regards

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Dear Bert,

Can I know your email address? I can send you the output file generated from Gaussian.

  • Bert Forum:Admin, Forum:Mod, NWChemDeveloper, bureaucrat, sysop
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bert.dejong@pnnl.gov

Quote: Jan 6th 8:07 am
Dear Bert,

Can I know your email address? I can send you the output file generated from Gaussian.

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Input files
I have upload two input files that gives you the singlet broken symmetry solution for O3.

1) Using the "mixang" directive
http://www.nwchem-sw.org/images/O3_singl.nw

2) Using the fragment guess option
http://www.nwchem-sw.org/images/O3_af.nw

Cheers, Edo

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Quote:Edoapra Jan 6th 8:38 pm
I have upload two input files that gives you the singlet broken symmetry solution for O3.

1) Using the "mixang" directive
http://www.nwchem-sw.org/images/O3_singl.nw

2) Using the fragment guess option
http://www.nwchem-sw.org/images/O3_af.nw

Cheers, Edo



Dear Edo,

The examples are very cool. I will try them. Thanks a lot for your kind help!

  • Niri Forum:Admin, Forum:Mod, NWChemDeveloper, bureaucrat, sysop
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Hi,

You will get <S2> = 0.5719 with Edo's input files. These are with B3LYP.
I am curious how you got <S2>=0.414265 with Gaussian. Did you use pure HF ?

Cheers,
-Niri

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Edo, we need to document the adapt keyword in the manual

Bert

Quote:Edoapra Jan 6th 8:38 pm
I have upload two input files that gives you the singlet broken symmetry solution for O3.

1) Using the "mixang" directive
http://www.nwchem-sw.org/images/O3_singl.nw

2) Using the fragment guess option
http://www.nwchem-sw.org/images/O3_af.nw

Cheers, Edo

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Quote:Niri Jan 10th 1:08 am
Hi,

You will get <S2> = 0.5719 with Edo's input files. These are with B3LYP.
I am curious how you got <S2>=0.414265 with Gaussian. Did you use pure HF ?

Cheers,
-Niri



With gaussian, you can use stable=opt in the input file, then the software automatically find the open shell singlet state.

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Hi Niri,

I notice that, if you optimize the structure with the open-shell singlet, you get nearly the same
spin-contamination <S2>=0.414265 of Gaussian09. I think the structure of open-shell singlet is similar
to triplet than singlet.

Shahab
Edited On 2:07:23 AM PDT - Tue, Sep 3rd 2013 by Shahabnaghavi
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S. Shahab Naghavi
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Scuola Internazionale Superiore di Studi Avanzati
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