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Re^4: CIS optimization state energy moves unreasonably

Jim Kress

Try doing a NBO analysis.  Then select your active space from the set of NBOs (or even NLMOs) that correspond to the atoms and/or bonds of primary concern to you.

This is how I usually set-up my MCSCF/ CASSCF calculations.


On Wed Jul 28 '10 3:15am, sanya wrote
>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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