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Re: Why the MCSCF calculation drops the n orbital from active space?

Alex Granovsky

Dear Panwang Zhou,

In fact this is very logical result. To keep n orbital in active space
you need to allow this orbital to correlate with another orbital in
the active space. There are two ways how you can arrange this: you can
either perform SA-MCSCF to capture n-pi* excited state or to add the
corresponding n* orbital to the active space.

Kind regards,
Alex Granovsky

On Wed Mar 18 '15 10:04am, Panwang Zhou wrote
>Dear all,

>Recently I carried out MCSCF calculations on a molecule where the n->pi* transition plays an important role. I selected the several lowest pi and pi* orbitals and the n orbital on the O atom of C=O group from the HF MOs. However, both the obtained MCSCF natural orbitals and MOs did not contain the n orbital. I have tested the CAS(10,9), CAS(12,11),CAS(12,10) calculations, all the optimized MCSCF orbitals drop the n orbital to the highest core orbital. This is unreasonable and I don't know why this occurs.

>As an example, I supplied the input and output files of CAS(12,11) calculation results in the attachment.

>Best Regards!


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