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

Abstract

We discuss the system-specific optimization of long-range separated density functional theory (DFT) for the prediction of electronic properties relevant for a photocatalytic cycle based on an Ir(III) photosensitizer (IrPS). Special attention is paid to the charge-transfer properties, which are of key importance for the photoexcitation dynamics, but and cannot be correctly described by means of conventional DFT. The optimization of the rangeseparation parameter using the ∆SCF method is discussed for IrPS including its derivatives and complexes with electron donors and acceptors used in photocatalytic hydrogen production. Particular attention is paid to the problems arising for a description of medium effects by means of a polarizable continuum model.

Chemical Tuning and Absorption Properties of Iridium Photosensitizers for Photocatalytic Applications

“…For the parent IrPS, its complexes with silver clusters, triethylamine, and iron carbonyls, a similar value of about 0.18 bohr −1 has been obtained previously [11,28,31]. LC-BLYP with optimal ω was shown to provide the best agreement with experimental spectra of the oxidized and reduced IrPS and, simultaneously, to increase the triplet stability of the ground state solution, which is essential for the accuracy of the excited states energies [31]. The obtained value is notably smaller than standard ω parameters (0.33 bohr −1 [34] and 0.47 bohr −1 [35]) obtained for training sets of atoms or small molecules and implemented as default values in quantum-chemical codes.…”

“…For all PSs studied in this work ω was found to be 0.17-0.19 bohr −1 . For the parent IrPS, its complexes with silver clusters, triethylamine, and iron carbonyls, a similar value of about 0.18 bohr −1 has been obtained previously [11,28,31]. LC-BLYP with optimal ω was shown to provide the best agreement with experimental spectra of the oxidized and reduced IrPS and, simultaneously, to increase the triplet stability of the ground state solution, which is essential for the accuracy of the excited states energies [31].…”

“…It ensures that Koopmans' theorem is fulfilled for the highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO) [53,56,57]. The details of the particular implementation of the protocol applied here can be found elsewhere [31].…”

Description of the Charge Transfer States at the Pentacene/C60 Interface: Combining Range-Separated Hybrid Functionals with the Polarizable Continuum Model

“…However, the soundness of such a DFT/ω(PCM)/PCM approach has been questioned. 21,22 For instance, it was found that this approach underestimates the energies of intra-molecular CT states. More recently, de Queiroz and Kümmel 23 proposed an approach that explicitly includes the solvent molecules into the tuning procedure.…”

“…In order to get a better understanding of the role that the interplay between the medium effect and the choice of the RS parameter plays on the system energetics, we illustrate in Figure 2 21,22 shows that the interaction with the dielectric medium (at least in the PCM approach used here) has only a minor effect on the orbital energies for all values of ω (the red and black lines corresponding to the HOMO and LUMO values are basically superimposed in Figure 2); however, the dielectric medium has a significant effect on, and markedly shifts the IP and EA values. In contrast, the orbital energies depend very strongly on the value of the RS parameter while the IP and EA show only a moderate dependence on ω.…”