We present an application of the ∆ self-consistent field (∆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
∆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 gasphase
to results from time-dependent density functional theory (TDDFT)
and experiments. To reproduce a typical dye-sensitised solar cell interface,
we adsorb cyanidin on TiO2 anatase (101), focussing 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
