title: Describing Excited State Relaxation and Localization in TiO2 Nanoparticles Using TD-DFT.
abstract: We have investigated the description of excited state relaxation in naked and hydrated TiO2 nanoparticles using Time-Dependent Density Functional Theory (TD-DFT) with three common hybrid exchange-correlation (XC) potentials: B3LYP, CAM-B3LYP and BHLYP. Use of TD-CAM-B3LYP and TD-BHLYP yields qualitatively similar results for all structures, which are also consistent with predictions of coupled-cluster theory for small particles. TD-B3LYP, in contrast, is found to make rather different predictions; including apparent conical intersections for certain particles that are not observed with TD-CAM-B3LYP nor with TD-BHLYP. In line with our previous observations for vertical excitations, the issue with TD-B3LYP appears to be the inherent tendency of TD-B3LYP, and other XC potentials with no or a low percentage of Hartree-Fock like exchange, to spuriously stabilize the energy of charge-transfer (CT) states. Even in the case of hydrated particles, for which vertical excitations are generally well described with all XC potentials, the use of TD-B3LYP appears to result in CT problems during excited state relaxation for certain particles. We hypothesize that the spurious stabilization of CT states by TD-B3LYP even may drive the excited state optimizations to different excited state geometries from those obtained using TD-CAM-B3LYP or TD-BHLYP. Finally, focusing on the TD-CAM-B3LYP and TD-BHLYP results, excited state relaxation in small naked and hydrated TiO2 nanoparticles is predicted to be associated with a large Stokes' shift.
authors.affiliation: Department of Chemistry, University College London , 20 Gordon Street, WC1H 0AJ London, U.K.
authors.forename: Enrico
authors.initials: E
authors.lastname: Berardo
authors.affiliation: William R. Wiley Environmental Molecular Science Laboratory, Battelle, Pacific Northwest National Laboratory , K8-91, P.O. Box 999, Richland, Washington 99352, United States.
authors.forename: Han-Shi
authors.initials: HS
authors.lastname: Hu
authors.affiliation: William R. Wiley Environmental Molecular Science Laboratory, Battelle, Pacific Northwest National Laboratory , K8-91, P.O. Box 999, Richland, Washington 99352, United States.
authors.forename: Hubertus J J
authors.initials: HJ
authors.lastname: van Dam
authors.affiliation: Department of Chemistry, University College London , 20 Gordon Street, WC1H 0AJ London, U.K.
authors.forename: Stephen A
authors.initials: SA
authors.lastname: Shevlin
authors.affiliation: Department of Chemistry, University College London , 20 Gordon Street, WC1H 0AJ London, U.K.
authors.forename: Scott M
authors.initials: SM
authors.lastname: Woodley
authors.affiliation: William R. Wiley Environmental Molecular Science Laboratory, Battelle, Pacific Northwest National Laboratory , K8-91, P.O. Box 999, Richland, Washington 99352, United States.
authors.forename: Karol
authors.initials: K
authors.lastname: Kowalski
authors.affiliation: Department of Chemistry, University College London , 20 Gordon Street, WC1H 0AJ London, U.K.
authors.forename: Martijn A
authors.initials: MA
authors.lastname: Zwijnenburg