Theoretical Study of Singlet Oxygen Molecule Generation via an Exciplex with Valence-Excited Thiophene

Singlet-oxygen [O₂(¹Δ_g)] generation by valence-excited thiophene (TPH) has been investigated using multireference Møller–Plesset second-order perturbation (MRMP2) theory of geometries optimized at the complete active space self-consistent field (CASSCF) theory level. Our results indicate that triplet TPH­(1³B₂) is produced via photoinduced singlet TPH­(2¹A₁) because 2¹A₁ TPH shows a large spin–orbit coupling constant with the first triplet excited state (1³B₂). The relaxed TPH in the 1³B₂ state can form an exciplex with O₂(³Σ_g^–) because this exciplex is energetically more stable than the relaxed TPH. The formation of the TPH­(1³B₂) exciplex with O₂(³Σ_g^–) whose total spin multiplicity is triplet (T₁ state) increases the likelihood of transition from the T₁ state to the singlet ground or first excited singlet state. After the transition, O₂(¹Δ_g) is emitted easily although the favorable product is that from a 2 + 4 cycloaddition reaction

Possible Polymerization of PS₄ at a Li₃PS₄/FePO₄ Interface with Reduction of the FePO₄ Phase

An important issue about developing all solid-state Li-ion batteries is to lower the high ionic interfacial resistance between a cathode and an electrolyte. An origin of the interfacial resistance is hypothesized due to a Li-depleted layer at the interface. Our computation has shown that the Li-depleted layer was the result of redox reaction at the interface in the charging process. In this subsequent theoretical study, we validate this redox reaction between the FePO₄ phase and the Li₃PS₄ phase from the viewpoint of their band alignment through the density functional theory with the hybrid functional (HSE06). In addition, we demonstrate that the Li-depleted layer grows up to a defective layer at a Li₃PS₄/FePO₄ interface by exothermic radical polymerization of PS₄ anions in the oxidized Li₃PS₄ phase with the volume reduction. This decrease in Li-ion sites due to the PS₄ polymerization makes the Li-depleted region long-lived and has the potential as an origin of the resistance against the Li-ion diffusion near the interface

QCforever: A Quantum Chemistry Wrapper for Everyone to Use in Black-Box Optimization

To obtain observable physical or molecular properties such as ionization potential and fluorescent wavelength with quantum chemical (QC) computation, multi-step computation manipulated by a human is required. Hence, automating the multi-step computational process and making it a black box that can be handled by anybody are important for effective database construction and fast realistic material design through the framework of black-box optimization where machine learning algorithms are introduced as a predictor. Here, we propose a Python library, QCforever, to automate the computation of some molecular properties and chemical phenomena induced by molecules. This tool just requires a molecule file for providing its observable properties, automating the computation process of molecular properties (for ionization potential, fluorescence, etc.) and output analysis for providing their multi-values for evaluating a molecule. Incorporating the tool in black-box optimization, we can explore molecules that have properties we desired within the limitation of QC computation

Theoretically Designed Li₃PO₄ (100)/LiFePO₄ (010) Coherent Electrolyte/Cathode Interface for All Solid-State Li Ion Secondary Batteries

Controlling the electrolyte/electrode interface is of great importance to promote new-generation solid-state Li ion secondary batteries. In this paper, we report a theoretically designed electrolyte/cathode coherent interface at the density functional theory level, where γ-Li₃PO₄ and LiFePO₄ are used as an electrolyte and a cathode, respectively. At the stoichiometric Li₃PO₄ (100)/LiFePO₄ (010) coherent interface, there are vacant Li-sites that give the chance for Li ions to migrate. From the density functional molecular dynamics at 1500 K, it is found that this interface is stable and no impurity phase is produced, and also that Li ions in the Li₃PO₄ phase around the interface can diffuse with large diffusion coefficients. The dynamic behavior of these Li ions is also reflected in the layered phonon spectra of Li ions; the diffusible Li ions around the interface have the same spectrum

Redox Reaction Mechanisms with Non-triiodide Mediators in Dye-Sensitized Solar Cells by Redox Potential Calculations

We investigate reaction mechanisms of the redox mediators in dye-sensitized solar cells through systematic calculations of redox potentials of possible cobalt complexes and iodides in acetonitrile solution by use of the thermodynamic cycle method with continuum solvent model. The calculated redox potentials were in good agreement with the experimental values, although the experimentalists used different reference electrodes. The maximum open circuit voltage (<i>V</i>_OC) of the mediators calculated in this work indicate that the I₂^•–/2I^– and I₂/I₂^•– as well as the net I₂/2I^– redox reactions can dominate at both photoanode and counter-electrode

Calorimetric Study of Glass Transition in Molecular Liquids Consisting of Globular Associates: Dicyclorohexylmethanol and Tricyclohexylmethanol

Heat capacities of liquids and liquid-quenched glasses (LQGs) of dicyclorohexylmethanol (DCHM) and tricyclohexylmethanol (TCHM) were measured by adiabatic calorimetry. Upon cooling the liquid compounds, they undergo glass transitions around 250 and 265 K, respectively. Temperature dependence of the FT-IR spectrum of TCHM liquid showed the gradual formation of dimers in the supercooled state with decreasing temperature. The magnitude of heat capacity jump at glass transition is discussed through a comparison with other low-molecular mass LQG. Combining the present results with previous heat capacity results on crystalline TCHM, residual entropies of LQG and standard thermodynamic quantities are established for both compounds

Effects of the lateral substituent on the cubic phase formation of two analogous compounds, 4ʹ-<i>n</i>-hexadecyloxy-3ʹ-cyanobiphenyl-4-carboxylic acid (ACBC-16) and its 3ʹ-nitro compound (ANBC-16)

<div><p>Two cubic (Cub) phase forming compounds, 4ʹ-<i>n</i>-hexadecyloxy-3ʹ-cyanobiphenyl-4-carboxylic acid (ACBC-16) and its 3′-nitro analogue (ANBC-16) were studied by infrared (IR) spectroscopy. In the temperature region of the Cub phase, the molar fraction of hydrogen-bonded COOH groups estimated for ACBC-16 was by ≈0.05 at maximum larger than that for ANBC-16 and the aromatic ring C═C stretching (ν(C═C)_ring) band frequency of ACBC-16 was by 3 cm⁻¹ lower than that of ANBC-16. The quantum chemical calculation at DFT/B3LYP level, on the one hand, showed no meaningful difference in the stabilisation energy for dimerisation and the ν(C═C)_ring band frequency between the respective model compounds. These results can be ascribed to the different steric effects of the side groups; the CN group would make possible the close contact of neighbouring phenyl rings while the bulky NO₂ group would not, giving slightly more stabilised dimerisation of ACBC-16 in the Cub phase than in ANBC-16.</p></div

Acetonitrile Solution Effect on Ru N749 Dye Adsorption and Excitation at TiO₂ Anatase Interface

We investigated stable structures and photoexcitation character of Ru N749 dye (black dye (BD)) adsorption to TiO₂ anatase (101) interface immersed in bulk acetonitrile (AN) solution, a most representative electrode interface in dye-sensitized solar cells (DSCs). Density-functional-theory-based molecular dynamics (DFT-MD) with explicit solvent molecules was used to take into account the fluctuations of solvation shells and adsorbed molecules. We demonstrated that BD adsorption via deprotonated carboxylate two anchors (d2) is the most stable at the interface, while the one protonated carboxyl anchor (p1) has the average energy only slightly higher than the d2. This indicates that the p1 state can still coexist with the d2 under equilibrium. It is in contrast with the calculated large stability of the p1 in vacuo. Inhomogeneous charge distribution and anchor fluctuation enhanced by AN solution causes this d2 stabilization. The calculated projected densities of states and the photoabsorption spectra clearly show that the d2 state has larger driving force of the electron injection into the TiO₂, whereas the photoabsorption in the wavelength region over 800 nm, a characteristic of BD sensitizer, is mainly attributed to the p1 state even in the AN solution. Consequently, the better performance of BD DSC can be understood in terms of the cosensitizer framework of the d2 and p1 states

Koopmans’ Theorem-Compliant Long-Range Corrected (KTLC) Density Functional Mediated by Black-Box Optimization and Data-Driven Prediction for Organic Molecules

Density functional theory (DFT) is a significant computational tool that has substantially influenced chemistry, physics, and materials science. DFT necessitates parametrized approximation for determining an expected value. Hence, to predict the properties of a given molecule using DFT, appropriate parameters of the functional should be set for each molecule. Herein, we optimize the parameters of range-separated functionals (LC-BLYP and CAM-B3LYP) via Bayesian optimization (BO) to satisfy Koopmans’ theorem. Our results demonstrate the effectiveness of the BO in optimizing functional parameters. Particularly, Koopmans’ theorem-compliant LC-BLYP (KTLC-BLYP) shows results comparable to the experimental UV-absorption values. Furthermore, we prepared an optimized parameter dataset of KTLC-BLYP for over 3000 molecules through BO for satisfying Koopmans’ theorem. We have developed a machine learning model on this dataset to predict the parameters of the LC-BLYP functional for a given molecule. The prediction model automatically predicts the appropriate parameters for a given molecule and calculates the corresponding values. The approach in this paper would be useful to develop new functionals and to update the previously developed functionals

Koopmans’ Theorem-Compliant Long-Range Corrected (KTLC) Density Functional Mediated by Black-Box Optimization and Data-Driven Prediction for Organic Molecules

Density functional theory (DFT) is a significant computational tool that has substantially influenced chemistry, physics, and materials science. DFT necessitates parametrized approximation for determining an expected value. Hence, to predict the properties of a given molecule using DFT, appropriate parameters of the functional should be set for each molecule. Herein, we optimize the parameters of range-separated functionals (LC-BLYP and CAM-B3LYP) via Bayesian optimization (BO) to satisfy Koopmans’ theorem. Our results demonstrate the effectiveness of the BO in optimizing functional parameters. Particularly, Koopmans’ theorem-compliant LC-BLYP (KTLC-BLYP) shows results comparable to the experimental UV-absorption values. Furthermore, we prepared an optimized parameter dataset of KTLC-BLYP for over 3000 molecules through BO for satisfying Koopmans’ theorem. We have developed a machine learning model on this dataset to predict the parameters of the LC-BLYP functional for a given molecule. The prediction model automatically predicts the appropriate parameters for a given molecule and calculates the corresponding values. The approach in this paper would be useful to develop new functionals and to update the previously developed functionals