Dynamic electron correlation effects on the ground state potential energy surface of a retinal chromophore model

Samer Gozem, Mark Huntress, Igor Schapiro, Roland Lindh, Alexander A. Granovsky, Celestino Angeli, Massimo Olivucci*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

143 Scopus citations


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.

Original languageAmerican English
Pages (from-to)4069-4080
Number of pages12
JournalJournal of Chemical Theory and Computation
Issue number11
StatePublished - 13 Nov 2012
Externally publishedYes


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