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Re: CASSCF

Amir Nasser Shamkhali
amir_n_shamkhali@yahoo.com

Dear Dave
For CASSCF calculations you should specify the active space orbitals. Also you should determine the number of electrons in these active orbitals. As the number of active orbitals and their containing electrons increases, you need more CPU time and momory. Usually for most of the molecules only HOMO-1, HOMO, LUMO, and LUMO+1 orbitals are taken into account as active space. Thus I think that information about the all of excitations are not necessary for first calculation. However, these information previously can be determined form a TDDFT calculation with a lower computational cost.

On Sun Feb 27 '11 8:18am, dave wrote
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>hi firefly

>i am about to study exited state systems and will use CASSCF as method, is it necessary for me to know the transitions involved in doing a CASSCF calculation? because the electronic transitions involved in the system have not been studied yet..i really need your help..thanks!

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