title: Dynamic Electron Correlation Effects on the Ground State Potential Energy Surface of a Retinal Chromophore Model.
abstract: The ground state potential energy surface of the retinal chromophore of visual pigments (e.g., bovine rhodopsin) features a low-lying conical intersection surrounded by regions with variable charge-transfer and diradical electronic structures. This implies that dynamic electron correlation may have a large effect on the shape of the force fields driving its reactivity. To investigate this effect, we focus on mapping the potential energy for three paths located along the ground state CASSCF potential energy surface of the penta-2,4-dieniminium cation taken as a minimal model of the retinal chromophore. The first path spans the bond length alternation coordinate and intercepts a conical intersection point. The other two are minimum energy paths along two distinct but kinetically competitive thermal isomerization coordinates. We show that the effect of introducing the missing dynamic electron correlation variationally (with MRCISD) and perturbatively (with the CASPT2, NEVPT2, and XMCQDPT2 methods) leads, invariably, to a stabilization of the regions with charge transfer character and to a significant reshaping of the reference CASSCF potential energy surface and suggesting a change in the dominating isomerization mechanism. The possible impact of such a correction on the photoisomerization of the retinal chromophore is discussed.
authors.affiliation: Department of Chemistry, Bowling Green State University, Bowling Green, Ohio 43403, United States.
authors.forename: Samer
authors.initials: S
authors.lastname: Gozem
authors.affiliation: Department of Chemistry, Bowling Green State University, Bowling Green, Ohio 43403, United States.
authors.forename: Mark
authors.initials: M
authors.lastname: Huntress
authors.affiliation: Department of Chemistry, Bowling Green State University, Bowling Green, Ohio 43403, United States.
authors.forename: Igor
authors.initials: I
authors.lastname: Schapiro
authors.affiliation: Department of Chemistry - Ångström, the Theoretical Chemistry Programme, POB 518, SE-751 20 Uppsala, Sweden.
authors.forename: Roland
authors.initials: R
authors.lastname: Lindh
authors.affiliation: Firefly Project, Moscow 117593, Russia.
authors.forename: Alexander A
authors.initials: AA
authors.lastname: Granovsky
authors.affiliation: Dipartimento di Chimica, Università di Ferrara, via Borsari 46, I-44121 Ferrara, Italy.
authors.forename: Celestino
authors.initials: C
authors.lastname: Angeli
authors.affiliation: Department of Chemistry, Bowling Green State University, Bowling Green, Ohio 43403, United States.|Dipartimento di Chimica, Università di Siena, via De Gasperi 2, I-53100 Siena, Italy.
authors.forename: Massimo
authors.initials: M
authors.lastname: Olivucci