Restricted open-shell Kohn–Sham theory for π–π* transitions. I. Polyenes, cyanines, and protonated imines

We present a self-consistent field algorithm for the restricted open-shell Kohn–Sham method which can be used to calculate excited states that have the same spatial symmetry as the corresponding ground states. The method is applied to π–π* transitions in polyenes, cyanines, and protonated imines. Excitation energies obtained with gradient corrected functionals are found to be significantly redshifted; the shift is constant within a homologous series. Planar excited state geometries have been optimized for all systems.