Ab initio molecular dynamics of retinals

A Car-Parrinello ab initio molecular dynamics calculation is presented of all-trans and 11-cis retinals. The minimum energy configurations of the two isomers have been determined by a simulated annealing procedure. The backbone conjugation is properly described within the local density approximation. The vibrational frequencies have been determined from the molecular dynamics trajectories. The theoretical results show an excellent agreement with experiment and provide grounds for an analysis of the retinal vibrations in terms of localized modes.