[attached MS-Word table was checked by jkl/a\ccl.net and seems OK] Dear Marcin, thanks for your reply. I have also worked on neutral systems and I am aware of the papers by Roos et al. The funny thing is that the agreement between CASSCF, TDHF, and TDDFT is amazing for closed shell cations. Maybe the more compact electron density changes the situation. The discrepancy starts only with the oscillator strength of the open-shell systems. If you like have a look at the table in the attachment. Best wishes, Ulrike On Wed, 2006-02-01 at 21:40 -0500, Marcin Makowski makowskma/chemia.uj.edu.pl wrote: > Sent to CCL by: "Marcin Makowski" [makowskm|a|chemia.uj.edu.pl] > Dear Ulrike, > > TDDFT usually gives wrong description of relative enegies of A_g and B_u > states of neutral polyenes. There was a paper by Head-Gordon showing that > Tamm-Dancoff approximation to TDDFT works better in this case than popular > RPA, but still this does not seem to be a method of choice for these > systems, probably. CASSCF worked quite fine as long as large active space > can be used. I remember one paper pointing that you need sth like > double-zeta active space (for octatetraene it would be 4 occupied, 8 > virtual) to obtain very good accuracy. I can search for reference if you > are interested. It was so as I've checked up to C10. I was testing some > time ago CIS(D) and SAC-CI but they still had big problems with A_g state > (the one dominated by double excitation). The similar problems might > happen for cations - this is out of my knowledge (I did not make any > calculations on them). > > > Yours, > Marcin Makowski > > -- Ulrike Salzner Associate Professor Department of Chemistry Bilkent University 06800 Bilkent, Ankara Turkey
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