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Matthieu Sala
matthieu.sala@u-bourgogne.fr

Dear Alex,

Thank you for answering this fast.

From what you say, I understand that relaxed dipole moments are more accurate than expectation-value ones. Is that correct ?

However, as I said I am interested in excited state polarizability for which I don't expect to get very accurate results from CASSCF.
Indeed we have compared CASSCF (with molpro), zero-order QDPT, MRCI (with molpro) and XMCQDPT2 (by double energy differentiation) and found that dynamic correlation is important.

Therefore expectation-value dipole would be sufficient four our purpose and an input example would be of great help.

I attach an input file for pyrazine which we are studying. It has zero dipole moments but we are interested in a field induced dipole so it is a RUNTYP=FFIELD input. I know that I don't use the fastest options for CASSCF and XMCQDPT2 but I like the fullnr and guga combination because it converges well and in this case it remains quite fast.

I would like to add a comment on zero-order QDPT transition moments.

In a previous post I was concern with the ZO-QDPT TDMs for aniline, I found that when the XMCQDPT2 model space contains only the states included in the SA-CASSCF part then I obtained good ZO-QDPT TDMs (the same as the CASSCF ones). However when the model space size was increased to include important contributions from higher states then the TDM for the 2nd pipi* excited state was very bad. You sent me a corrected input that did not change the problem (although it was useful for me as an example for good XMCQDPT2 calculations.)

I find the same behaviour in pyrazine. When increasing the size of the model space the TDM for the third excited state (first pipi*) again become very bad.

I just wanted to bring this to your attention.

Thank you for your help and comments.
Best regards.

Matthieu


>Dear Matthieu,

>Do you need relaxed or expectation-value dipole moments?

>Relaxed dipole moments could be computed using the same
>approach as the one used by SA-CASSCF gradient code, namely,
>by differentiation of state-averaged dipole moment
>with respect to a state weight. This is because the differentiation
>of averaged one and two particle density matrices with respect to
>a state weight produces response-type state-specific density
>matrices. This is the most general and powerful statement related
>to such a differentiation which allows computation of state-specific
>gradients and any one and two-electron properties using such
>differentiation.

>If you can wait a month or so, the code for relaxed dipole moments
>will be available as a part of Firefly.

>Computation of expectation-value state-specific dipole moments is
>even simpler. The dipole moments of this type can be computed
>by the present code. If this is the type of dipole moments you need,
>please let me know and I'll post sample input file.

>Kind regards,
>Alex Granovsky
>
>
>On Wed Mar 27 '13 7:05pm, Matthieu Sala wrote
>---------------------------------------------
>>Dear Firefly users,

>>I would like to know if there is a way to compute excited state dipole moments from a state averaged CASSCF calculation in Firefly.

>>The reason is that I would like to compute excited state polarizabilities by finite differentiation of the dipole rather than double differentiation of the energy with respect to an applied field.

>>I know that I can obtain zero order QDPT dipole moments from a XMCQDPT2 calculation and that these might be better than CASSCF although not of full XMCQDPT2 quality. However I would like to compute pure CASSCF dipole moments, at least for the purpose of comparison.

>>Best regards.
>>Matthieu Sala

This message contains the 515 kb attachment [ pyr_ffield_xmcqdpt2.inp ]