Employing density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations in combination with the semiclassical nuclear ensemble method, we have simulated the photoabsorption spectra of the four canonical DNA nucleobases in aqueous solution. In order to model the effects of solvation, for each nucleobase, a number of solvating water molecules were explicitly included in the simulations, and additionally, the bulk solvent was represented by a continuous polarizable medium. We find that the effect of the solvation shell in general is significant, and its inclusion improves the realism of the spectral simulations. The involvement of lone electron pairs in the hydrogen bonding with the solvating water molecules has the effect of systematically increasing the energies of vertical excitation into the nπ∗-type states. Apart from a systematic blue shift of around 0.3eV observed in the absorption peaks, the calculated photoabsorption spectra reproduce the measured ones with good accuracy. The photoabsorption spectra are dominated by excited states with ππ∗and partial ππ∗character. No low-energy charge transfer states are observed with the use of the CAM-B3LYP and M06-2X functionals.
Employing density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations in combination with the semiclassical nuclear ensemble method, we have simulated the photoabsorption spectra of the four canonical DNA nucleobases in aqueous solution. In order to model the effects of solvation, for each nucleobase, a number of solvating water molecules were explicitly included in the simulations, and additionally, the bulk solvent was represented by a continuous polarizable medium. We find that the effect of the solvation shell in general is significant, and its inclusion improves the realism of the spectral simulations. The involvement of lone electron pairs in the hydrogen bonding with the solvating water molecules has the effect of systematically increasing the energies of vertical excitation into the nπ∗-type states. Apart from a systematic blue shift of around 0.3eV observed in the absorption peaks, the calculated photoabsorption spectra reproduce the measured ones with good accuracy. The photoabsorption spectra are dominated by excited states with ππ∗ and partial ππ∗ character. No low-energy charge transfer states are observed with the use of the CAM-B3LYP and M06-2X functionals.