Charge-Transfer Excited States in a π-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.

Tuning Range-Separated Density Functional Theory for Photocatalytic Water Splitting Systems

“…20,35,40,42,50,52,53,[59][60][61][65][66][67][68][69][70][71][72][73][74][75][76][77][78][79][80][81][82] The accuracy of optimally tuned range-separated functionals was critically tested in ref 61 for basis set variation as well as prediction of relative energies of spin states, binding energies, and the form of potential energy surfaces.…”

Electronic excitations from a linear-response range-separated hybrid scheme

“…It has also been proposed to use in this scheme an empirically modified correlation density functional depending on the range-separation parameter [14]. The CAM-B3LYP scheme and other similar schemes have also been applied in linear-response theory for calculating excitation energies [11,[15][16][17][18][19][20][21][22][23][24][25][26]. In all these schemes, the presence of long-range HF exchange greatly improves Rydberg and charge-transfer excitation energies, in comparison to time-dependent Kohn-Sham (TDKS) calculations using standard local or semilocal density-functional approximations in which they are strongly underestimated (see, e.g., Ref.…”

Communication: Configuration interaction singles has a large systematic bias against charge-transfer states

“…[5][6][7][8][9] This failure of TD-DFT stems from the approximate (adiabatic) exchange-correlation functional, 10,11 and recent work in quantum chemistry has created new functionals that add in exact Hartree-Fock exchange at long-distance by partitioning the Coulomb operator. [12][13][14][15][16][17][18][19][20][21][22][23][24] These so-called longa) Electronic mail: subotnik@sas.upenn.edu.…”