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Re^4: MCSCF + PCM

lello
raffaele.borrelli@unito.it


I agree with your statements. However I have in mind a different
case for which state specific solvation can be of help such as the
calculation of electronic absorption bands (I am condidering
the simulation of the entire vibronic profile).spectroscopy
In that case one needs the equilibrium geometry of the
solute in both its ground and excited state and in both states
the solvent should be "in equilibrium" with the solute, i.e. the reaction field should be state specific.

I agree with you that increasing the weight of the state of interest
might be a solution, with the limiting case of a state-specific
MCSCF. This, I think, would be the best option, if possible.
However, in my experience it can be quite hard to achieve
convergence on a SS-MCSCF geometry optimization for an excited state,
unless one has symmetry labels to help the choice of the reference.
In those cases where SS-MCSCF won't converge, and I bet there
are many, SA-MCSCF + state-specific solvation gradients can be
a good compromise.

Lello


On Tue May 28 '13 6:36pm, Alex Granovsky wrote
----------------------------------------------
>Hello,

>>thanks for the reply. Actually it might be a good idea to
>>implement a state-specific solvation for MCSCF.
>>An interesting case is when a system has an excited state with
>>a charge-transfer character. In that case using an average density
>>might give an unexpected result, but I might be wrong.

>I do not agree with this. Consider SA-CASSCF over two states,
>the ground state with no charge-transfer and the first excited
>state of charge-transfer type. If one is using field generated
>by the averaged density then both states are not described
>very good. However, they are least approximately described
>on an equal footing. If one is using reaction field from the
>second state, at the first glance S1 state becomes much better
>described. At the same time the ground state becomes described
>very poorly. Even worse, because S0 is now not well described,
>in SA-MCSCF procedure S1 state will tend to partly mimic S0 state
>and thus, actually even S1 state will become not such a well described.

>Perhaps if one is interested in describing S1 state only,
>then this approach may work. However, I'd prefer just to
>increase to the weight of S1 state in state-averaging.

>>Concerning the gradients, is there a theoretical reason why
>>they should be disabled? or is it just a technical problem?

>Because at least at the first glance this modified MCSCF procedure  
>will not be longer compatible with our implementation of gradients
>for SA-MCSCF (http://classic.chem.msu.su/gran/gamess/ss-gradients.pdfhttp://classic.chem.msu.su/gran/gamess/ss-gradients.pdf).
>However, this may requre a more detailed analysis.

>Kind regards,
>Alex Granovsky
>
>
>


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