Conical intersections minimal models

The first study in which a full CASSCE treatment was used for the non-adiabatic dynamics of a polyatomic system was a study on a model of the retinal chromophore [86]. The cis-trans photoisomerization of retinal is the primary event in vision, but despite much study the mechanism for this process is still unclear. The minimal model for retinal is l-cis-CjH NHj, which had been studied in an earlier quantum chemisti7 study [230]. There, it had been established that a conical intersection exists between the Si and So states with the cis-trans defining torsion angle at approximately a = 80° (cis is at 0°). Two... 

Fig. 2 Schematic representation of the Si /Sq conical intersection seam along the torsion coordinate of the central bond of the minimal retinal chromophore model pentadieniminium cation (reprinted with permission from [20])...

Fig. 12.4. Energy profiles along the Si photoisomerization coordinate of a PSBll minimal model at CASPT2//CASSCF and TD-DFT//CASSCF levels of theory. Notice that both the reaction paths and the conical intersection family are qualitatively described at the TDDFT levels (redrawn with permission from Ref. [28] 2004 American Chemical Society).

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