A dressed TDDFT treatment of the 21Ag states of butadiene and hexatriene

The nature and energetics of the low-lying singlet states of polyenes have presented significant challenges for electronic structure methods. This is particularly true for conventional implementations of time-dependent density functional theory (TDDFT), which, because of their use of the adiabatic approximation, have difficulty in describing states of `doubly-excited characterʹ. We show that use of our recently developed `Dressed TDDFTʹ approach provides a compact and accurate method for treating these doubly excited states, by use of a frequency-dependent exchange-correlation kernel. We present results for the vertical absorption energy for the 21Ag states of butadiene and hexatriene, and the vertical fluorescence and 0–0 transitions for the 21Ag state of butadiene.