Charge Transfer States of Aqueous B-DNA at Energies Above the Bright $^1\pi\pi^\ast$ Exciton States

Charge transfer states have been proposed to explain experimentally observed long-lived excited state dynamics in aqueous DNA oligomers\footnote{Crespo-Hern\'andez,~C.~E.;\ \ Cohen,~B.;Kohler,~B. \textit{Nature} \textbf{2005}, \textsl{436}, 1141.}. Due to the large number of atoms, tractably describing such excited states in DNA systems with \textit{ab initio} theory is limited to TD-DFT. However, standard TD-DFT exchange-correlation functionals significantly underestimate CT excitation energies owing to incorrect asymptotic behavior. To circumvent this error, we instead apply recently developed and optimized long-range corrected TD-DFT functionals to better assess the low lying CT and exciton states of DNA oligomers. We show that long-range corrected TD-DFT yields results comparable to correlated wave function models, placing CT states of aqueous B-DNA at energies above the optically bright $^1\pi\pi^\ast$ exciton states, contrary to TD-DFT results which find CT states below the exciton states.