Author Topic: Vibrational spectrum of first excited state  (Read 730 times)

luyj

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Vibrational spectrum of first excited state
« on: December 23, 2017, 03:45:43 pm »
Hello,

I calculated the vibrational spectrum of a small organic molecule at a transition state with aoforce, which worked fine. Then I went back and changed the electronic structure to the lowest triplet state (via eht). I repeated aoforce and the imaginary mode is missing. It apparently is now part of the real modes as the total number is the same.
I am very confident, that the structure is a transition state, as it describes an intramolecular hydrogen shift, but I want to know what changes when another electronic state is assumed. Since the excited state gradients work fine within jobex I assume it should also work with aoforce.

I am including the structure and the output.

Best regards and happy holidays.
« Last Edit: December 28, 2017, 05:50:21 pm by luyj »

uwe

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Re: Vibrational spectrum of first excited state
« Reply #1 on: December 28, 2017, 03:02:14 pm »
Hi,

which method and basis set did you use? If you also post the control file, it would be easier to reproduce your calculations.

Regards,

Uwe

luyj

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Re: Vibrational spectrum of first excited state
« Reply #2 on: December 28, 2017, 05:51:25 pm »
Hi,

sure I added the control file to the initial post.

Edit:

It seems that I have the same problem as the first post from this topic: http://www.turbo-forum.com/index.php?topic=823.0

A structure that very clearly is not a minimum turns out with no imaginary modes.
« Last Edit: January 04, 2018, 12:58:16 pm by luyj »

Arnim

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Re: Vibrational spectrum of first excited state
« Reply #3 on: January 08, 2018, 02:04:19 pm »
Hello,

I just ran energy and gradient calculations with your input and noticed that gradient for the triplet is not zero (also not for the singlet, btw). Therefore, this structure of course can not be a minimum of the triplet state, regardless of the second derivative.

Cheers,

Arnim

luyj

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Re: Vibrational spectrum of first excited state
« Reply #4 on: January 08, 2018, 02:57:34 pm »
Hello,

I just ran energy and gradient calculations with your input and noticed that gradient for the triplet is not zero (also not for the singlet, btw). Therefore, this structure of course can not be a minimum of the triplet state, regardless of the second derivative.

Cheers,

Arnim

Hello,

that is right I am looking for the transition state. To use statpt itrvec I need some guess for the imaginary mode, but there is none. The input structure is the TS of the singlet case.

Arnim

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Re: Vibrational spectrum of first excited state
« Reply #5 on: January 08, 2018, 03:17:43 pm »
When you are looking for a transition state with triplet occupation, you can do that similar to the singlet case.
Since you have computed already the Hessian of the triplet state, you could open the control file in TmoleX and visualize the vibrational frequencies. Then distort the molecule along the mode, which you can identify as your hydrogen transfer reaction mode and run jobex -trans for that structure.

Hope that helps,

Arnim