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Re: Doubts regarding TDDFT calculations and excited state determination....

Pavlo Solntsev
pavlo.solntsev@gmail.com

On Thu Sep 11 '14 7:21am, Siddheshwar Chopra wrote
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>Dear Firefly Users,

>I am stuck up with the concept of excited states. Specifically speaking with some doubts in TDDFT.

>What is meant by NSTATE in FIREFLY i/p file?

The number of states to be found, excluding the ground state. (Default is 1)

>I know ISTATE is singlet or doublet...

The state for which properties and/or the gradient will be calculated. Only one state
can be chosen. A negative sign may precede the state number; this will enable state
tracking for the state of interest. (Default is 1)

When I read the firefly TDDFT o/p file.. I see that for every EXCITED STATE, I have a set of probable transitions... THIS IS WHAT IS CONFUSING ME ...

What do expect? To see a pure transition from an orbital A to an orbital B? You always have a "contribution" from other transitions. Lets calla them micro-transition. If you have a system where single determinant approach works fine, you should be able to see major component with expansion coefficients close to 0.9.

>What I assumed till now is that first excited state is LUMO. But now in the firefly o/p file I see HOMO--> LUMO transitions occuring for almost all excited states 1,2,3 etc..

What about expansion coefficients? Are they the same for all states? If so, you probably have multireference character.

>So my concept of Excited state is unclear... I just open the TDDFT o/p fie with Gausssum and get the spectra.

I also get the probabilities of the particular transitions alongwith their osc. strengths. Probabilities must be calculated by squaring and adding the SAPs. But I can't visualize the excited state here. Please explain to me this.

FF prints all components for transition dipole moment. What does it meant to visualize excited state?

Also, it would be useful to see the output file.

Sincerely,
Pavlo.

>Kind Regards,

Thu Sep 11 '14 5:40pm