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Re^3: CIS optimization state energy moves unreasonably


On Tue Jul 27 '10 4:16pm, Jonas Baltrusaitis wrote
>From what I've read in the literature CASSCF should be a good thing for my molecules since it can deal with multireference character and bond breaking. I am a bit hesitant since I am not sure how to select the active space. Would TDDFT do in selecting which orbitals and electrons to correlate? Is there a rule of thumb?

DFT (as well as HF) orbitals are not very good as starting MOs. Natural orbitals are better. Unfortunately, there is no rule of thumb in selecting the active space, just a common sense and a chemical insight :) In fact, it is individual for each molecular system.

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