[CPMD-list] ROKS and TDDFT of spin polarized systems

[Juerg Hutter]

Hi

> Hello everyone,
>
>       Here I ask another question. I am studying the isomerization of a
> chromophore of a photoreceptor protein. I am doing that by calculating
> potential energy surfaces of the ground and first excited singlet state along
> the isomerization coordinate, the torsional angle around a double bond. I am
> calculating the excited states with ROKS and TDDFT. At the twisted angle of 90
> degrees in the ground state the double bond breaks and a spin unrestricted
> (LSD) calculation is necessary. My question is: how can I calculate the excited
> state of that structure?
>
> - I tried to do the calculation with TDDFT but only a mixed state was obtained.
> Is there the spin-unrestricted TDDFT implemented on CPMD?

Yes, there is. Use the LSD keyword and ask for MIXED STATES in the TDDFT
section.

>
> - ROKS is a spin restricted method, but could I somehow do different
> calculatiosn by transfering the electron at HOMO with spin-up and spin-down and
> then do a linear combination to get the right spin?
>

I don't get what you want to achieve with this. ROKS gives you a singlet
wavefunction in the excited state. It should also be able to handle
a biradical reasonably (see the literature for the ROSS method).

There have been several publications on double bond isomerisation using
ROKS and TDDFT. There you will find all the problems people have
encountered for this type of excited state reaction.

regards

Juerg Hutter


> Thank you very much for any hints or comments.
>
>         Regards,
>
>
>              Eneritz
>
>
> --
> Eneritz Muguruza
> eneritz.muguruza at kcl.ac.uk
>
>
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