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? I know ISTATE is singlet or doublet... NSTATE seems to be the no. of excited states I wish to study.. 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 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.. 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.