Molecular design of benzo[c][1,2,5]thiadiazole or thieno[3,4-d]pyridazine-based auxiliary acceptors through different anchoring groups in D-π-A-A framework: A DFT/TD-DFT study.

Based on density functional theory (DFT) and time-dependent DFT (TD-DFT) methods, a novel series of D-π-A-A porphyrin sensitizers adsorbed on the TiO2 cluster has been investigated. The D-π-A-A configurations contained a donor of iminodibenzyl, π-linker of Zn-porphyrin, and two kinds of auxiliary acceptors (labeled as BT and TP), as well as five types of anchoring groups. The ground-state geometries, electronics, optics, and charge transfer properties of all free dyes including injection driving force (ΔGinj), regeneration energy (ΔGreg), and light-harvesting efficiency (LHE) were calculated. Additionally, reorganization energy (λtotal), electron affinity (EA), and ionization potential (IP) were also reported to confirm the transport properties of the designed dye. Furthermore, the interfacial system of dye@(TiO2)48 was further discussed to reveal the complexation energy of the system by considering the adsorption energy (Eads) between dyes and (TiO2)48. The results showed that the insertion of different auxiliary acceptors in the D-π-A-A motif and variations in the anchoring groups resulted in red-shift absorption along with the increase in photovoltaic properties. These results suggested that BT with the rhodanine-3-acetic acid group (BT4) and BT with 2-(1,1-dicyanomethylene)rhodanine group (BT5) and TP with the same rhodanine-3-acetic acid and 2-(1,1-dicyanomethylene)rhodanine groups (TP4 and TP5) had shown better properties among other candidates for DSSCs. BT4-BT5 and TP4-TP5 had pronounce effect on optical and charge transfer properties by showing small HOMO-LUMO gaps, red-shifted spectra (λmax), greater LHE and ICT characters, and maximum-negative Eads. Thus, our theoretical investigation using these auxiliary moieties can be helpful for the precise structural modifications and design for developing efficient dyes in dye-sensitized solar cells (DSSCs).

Development of Density-Functional Tight-Binding Parameters for the Molecular Dynamics Simulation of Zirconia, Yttria, and Yttria-Stabilized Zirconia.

In this work, a set of density-functional tight-binding (DFTB) parameters for the Zr-Zr, Zr-O, Y-Y, Y-O, and Zr-Y interactions was developed for bulk and surface simulations of ZrO2 (zirconia), Y2O3 (yttria), and yttria-stabilized zirconia (YSZ) materials. The parameterization lays the ground work for realistic simulations of zirconia-, yttria-, and YSZ-based electrolytes in solid oxide fuel cells and YSZ-based catalysts on long timescales and relevant size scales. The parameterization was validated for the zirconia and yttria polymorphs observed under standard conditions based on density functional theory calculations and experimental data. Additionally, we performed DFTB-based molecular dynamics (MD) simulations to compute structural and vibrational properties of these materials. The results show that the parameters can give a qualitatively correct phase ordering of zirconia, where the tetragonal phase is more stable than the cubic phase at a lower temperature. The lattice parameters are only slightly overestimated by 0.05-0.1 Å (2% error), still within the typical accuracy of first-principles methods. Additionally, the MD results confirm that zirconia and yttria phases are stable against transformations under standard conditions. The parameterization also predicts that vibrational spectra are within the range of 100-1000 cm-1 for zirconia and 100-800 cm-1 for yttria, which is in good agreement with predictions both from full quantum mechanics and a recently developed classical force field. To further demonstrate the advantage of the developed DFTB parameters in terms of computational resources, we conducted DFTB/MD simulations of the YSZ4 and YS12 models containing approximately 750 atoms.