Δ Self-Consistent Field Method for Natural Anthocyanidin Dyes

We present an application of the Delta self-consistent field (Delta SCF) method, which we have implemented and tested in the DFT code CONQUEST, on the study of excited states of natural anthocyanidin dyes. We show that Delta SCF allows relaxation of the atomic structure for systems in excited states by following gradients on the excited Born-Oppenheimer surface. We compare the vertical excitation energies of some anthocyanidins in gas phase to results from time-dependent density functional theory (TDDFT) and experiments. To reproduce a typical dye-sensitized solar cell interface, we adsorb cyanidin on TiO2 anatase (101), focusing on the shift of the lowest excitation energy due to the adsorption. We have found that important modifications occur in the excited state geometry of the adsorbed cyanidin.