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 S0 and S1 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 S1 minimum energy path lying approximately halfway between the 11-cis and all-trans S1 minima. In this minimum on the S1 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 S1 minima.