Comparing long-range corrected functionals in the cis-trans isomerisation of the retinal chromophore

Earlier results for the 11-cis to all-trans isomerisation of the retinal chromophore after photoexcitation, studied using time-dependent density functional theory with the hybrid CAM-B3LYP functional, are compared with new results using other long-range corrected DFT functionals. The TDDFT S ₀ and S ₁ minimum energy paths have been compared with the approximate coupled-cluster method RI-CC2. All calculations were consistent in producing an additional avoided crossing minimum on the S ₁ minimum energy path lying approximately halfway between the 11-cis and all-trans S ₁ minima. In this minimum on the S ₁ potential energy surface, the retinal chromophore has inverted bond order in its carbon chain and lower energy than it has in both the 11-cis and all-trans S ₁ minima.