title: Charge-transfer excited states in a pi-stacked adenine dimer, as predicted using long-range-corrected time-dependent density functional theory.
abstract: The lowest few electronic excitations of a pi-stacked adenine dimer in its B-DNA geometry are investigated, in the gas phase and in a water cluster, using a long-range-corrected version of time-dependent density functional theory (TD-DFT) that asymptotically incorporates Hartree-Fock exchange. Long-range correction is shown to eliminate the catastrophic underestimation of charge-transfer (CT) excitation energies that plagues conventional TD-DFT, at the expense of introducing one adjustable parameter, mu, that determines the length scale on which Hartree-Fock exchange is turned on. This parameter allows us to interpolate smoothly between hybrid density functionals and time-dependent Hartree-Fock theory. Excitation energies for CT states (in which an electron is transferred from one adenine molecule to the other) are found to increase dramatically as a function of mu. Uncorrected hybrid functionals underestimate the CT excitation energies, placing them well below the valence excitations, while time-dependent Hartree-Fock calculations place these states well above the valence states. Values for mu determined from certain benchmark calculations place the CT states well above the valence pipi* and npi* states at the Franck-Condon point.
authors.affiliation: Department of Chemistry, The Ohio State University, Columbus, OH 43210, USA.
authors.forename: Adrian W
authors.initials: AW
authors.lastname: Lange
authors.forename: Mary A
authors.initials: MA
authors.lastname: Rohrdanz
authors.forename: John M
authors.initials: JM
authors.lastname: Herbert
mesh_terms: D000225:Adenine / Q000737:chemistry*; D019281:Dimerization; D008958:Models, Molecular
chemical_list: D000225:Adenine