Ceilidh ... Re^9: excited state geometry opt and intersystem crossing

Firefly and PC GAMESS-related discussion club

Re^9: excited state geometry opt and intersystem crossing

Jonas Baltrusaitis
jonas-baltrusaitis@uiowa.edu

On Sat Jun 12 '10 3:13am, Jonas Baltrusaitis wrote
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>On Sat Jun 12 '10 1:42am, sanya wrote
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>>>I disabled SOSCF and with DIIS it went through. I was wondering if there is any way to tell if it converged to the state I requested, e.g. if state tracking feature did its job
>>>By the same token, how did you find out that the system was nearly degenerate from the output?

>>SCF that converges or fails to converge is for the ground state. CIS procedure generates the excited states. Their energies should be no less than the ground state energy (variational principle). In your output, the energy of the first excited state decreased, while the ground state energy increased. In the step before SCF failed to converge, the energies of the ground and first excited states became close, so you might expect problems. Sooner or later, they would appear.

>>As for root tracking in CIS, this can be necessary for the excited states, which can easily flip. The manual says: The state-tracking feature of the PC GAMESS' CIS code can be activated by selecting negative value of istate in the $cis group. It is intended for geometry optimization of the excited states in the case of root flipping. This is not necessary for assumed flipping of the ground and excited state, because they never flip, they can only become degenerate, and this means that you should use MCSCF for your system.

>Thanks, that's much clearer. Believe it or not with DIIS enabled and SOSCF disabled I finished geometry optimizations successfully. I will have to examine the outputs for anything suspicious WRT first excited and ground state energies being close. I used state tracking so I assume it actually converged to first excited. Is there a way to check for that?

Well, this molecule really doesn't want to collaborate. I have not really worked with any of MCSCF and was hoping CIS or TDDFT would do. While I understand the princpiles of MCSCF, is there a guide on the website on how to setup MCSCF for my molecule, e.g. choose right parameteres in correlating orbitals and electrons.
Also, will any of the MCSCF methods will work efficiently for 76 atom moecule? Both optimization and frequencies in excited state or frequencies is not an option?

Sat Jun 12 '10 6:09am

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