Pentagon-Rich Caged Carbon Catalyst for the Oxygen Reduction Reaction in Acidic Electrolytes.

The interaction between electron spin and oxygen molecules in non-platinum catalysts, particularly carbon catalysts, significantly influences the catalytic performance of the oxygen reduction reaction (ORR). A promising approach to developing high-performance catalysts involves introducing five-membered ring structures with spin into graphitic carbons. In this study, we present the successful synthesis of cage-like cubic carbon catalysts enriched with pentagon structures using pentagon ring-containing C and a NaCl template.

Metal- and ligand-substitution-induced changes in the kinetics and thermodynamics of hydrogen activation and hydricity in a dinuclear metal complex.

Catalytic function in organometallic complexes is achieved by carefully selecting their central metals and ligands. In this study, the effects of a metal and a ligand on the kinetics and thermodynamics of hydrogen activation, hydricity degree of the hydride complex, and susceptibility to electronic oxidation in bioinspired NiFe complexes, [NiX Fe(Cl)(CO)Y] ([NiFe(Cl)(CO)]; X = ,'-diethyl-3,7-diazanonane-1,9-dithiolato and Y = 1,2-bis(diphenylphosphino)ethane), were investigated. The density functional theory calculations revealed that the following order thermodynamically favored hydrogen activation: [NiFe(CO)] > [NiRu(CO)] > [NiFe(CNMe)] ∼ [PdRu(CO)] ∼ [PdFe(CO)] ≫ [NiFe(NCS)].

Chemical modification of dimethylpolysiloxane for enhancement of CO binding enthalpy.

The intermittent increase in CO concentration in the atmosphere is a serious problem that contributes to climate change; the combustion of fossil fuels produces the majority of CO, and technology is needed to capture it efficiently. Various CO capture materials have been developed so far. Membrane separation, in particular, has an advantage over other capture technologies due to its ease of use.

Photochemical conversion of CO to CO by a Re complex: theoretical insights into the formation of CO and HCO from an experimentally detected monoalkyl carbonate complex.

Triethanolamine (TEOA) has been used for the photocatalytic reduction of CO, and the experimental studies have demonstrated that the TEOA increases the catalytic efficiency. In addition, the formation of a carbonate complex has been confirmed in the Re photocatalytic system where DMF and TEOA are used as solvents. In this study, we survey the reaction pathways of the photocatalytic conversions of CO to CO + HO and CO to CO + HCO by -Re(bpy)(CO)Br in the presence of TEOA using density functional theory (DFT) and domain-based local pair natural orbital coupled cluster approach, DLPNO-CCSD(T).

H activation by hydrogenase-inspired NiFe catalyst using frustrated Lewis pair: effect of buffer and halide ion in the heterolytic H-H bond cleavage.

Hydrogen is a clean fuel alternative to fossil fuels, and it is vital to develop catalysts for its efficient activation and production. We investigate the reaction mechanism of H activation in an aqueous solution by the recently developed NiFe complex (Ogo . 2020, 6, eaaz8181) using density functional theory (DFT) calculation.

Ionization Energies and Redox Potentials of Hydrated Transition Metal Ions: Evaluation of Domain-Based Local Pair Natural Orbital Coupled Cluster Approaches.

Hydrated transition metal ions are prototypical systems that can be used to model properties of transition metals in complex chemical environments. These seemingly simple systems present challenges for computational chemistry and are thus crucial in evaluations of quantum chemical methods for spin-state and redox energetics. In this work, we explore the applicability of the domain-based pair natural orbital implementation of coupled cluster (DLPNO-CC) theory to the calculation of ionization energies and redox potentials for hydrated ions of all first transition row (3d) metals in the 2+/3+ oxidation states, in connection with various solvation approaches.

Hydrogen evolution, electron-transfer, and hydride-transfer reactions in a nickel-iron hydrogenase model complex: a theoretical study of the distinctive reactivities for the conformational isomers of nickel-iron hydride.

Hydrogen fuel is a promising alternative to fossil fuel. Therefore, efficient hydrogen production is crucial to elucidate the distinctive reactivities of metal hydride species, the intermediates formed during hydrogen activation/evolution in the presence of organometallic catalysts. This study uses density functional theory (DFT) to investigate the isomerizations and reactivities of three nickel-iron (NiFe) hydride isomers synthesized by mimicking the active center of NiFe hydrogenase.

[NiFe], [FeFe], and [Fe] hydrogenase models from isomers.

The study of hydrogenase enzymes (Hases) is necessary because of their importance to a future hydrogen energy economy. These enzymes come in three distinct classes: [NiFe] Hases, which have a propensity toward H oxidation; [FeFe] Hases, which have a propensity toward H evolution; and [Fe] Hases, which catalyze H transfer. Modeling these enzymes has so far treated them as different species, which is understandable given the different cores and ligand sets of the natural molecules.

Selective Oxidation of H and CO by NiIr Catalyst in Aqueous Solution: A DFT Mechanistic Study.

One of the challenges in utilizing hydrogen gas (H) as a sustainable fossil fuel alternative is the inhibition of H oxidation by carbon monoxide (CO), which is involved in the industrial production of H sources. To solve this problem, a catalyst that selectively oxidizes either CO or H or one that co-oxidizes H and CO is needed. Recently, a NiIr catalyst [NiCl(X)IrCl(η-CMe)], (X = dimethyl-3,7-diazanonane-1,9-dithiolate), which efficiently and selectively oxidizes either H or CO depending on the pH, has been developed ( , 56, 9723-9726).

Ionization Energies and Aqueous Redox Potentials of Organic Molecules: Comparison of DFT, Correlated ab Initio Theory and Pair Natural Orbital Approaches.

The calculation of redox potentials involves large energetic terms arising from gas phase ionization energies, thermodynamic contributions, and solvation energies of the reduced and oxidized species. In this work we study the performance of a wide range of wave function and density functional theory methods for the prediction of ionization energies and aqueous one-electron oxidation potentials of a set of 19 organic molecules. Emphasis is placed on evaluating methods that employ the computationally efficient local pair natural orbital (LPNO) approach, as well as several implementations of coupled cluster theory and explicitly correlated F12 methods.

Photochemical ring opening and closing of three isomers of diarylethene: spin-flip time-dependent density functional study.

The reaction mechanism of photochemical ring opening and closing transformation was investigated for diarylethene (DAE), which works as a molecular switch and photodevice. Spin-flip time-dependent density functional theory is employed to map the potential energy surfaces and to elucidate the photochemical mechanism of three isomers (normal, inverse, and mixed types) of 1,2-dithienylethene, a model DAE. The potential energy characteristics including the minimum-energy conical intersection reveals the origin of different product preferences of the three isomers.

Complete active space second order perturbation theory (CASPT2) study of N(²D) + H₂O reaction paths on D₁ and D₀ potential energy surfaces: direct and roaming pathways.

We report reaction paths starting from N((2)D) + H2O for doublet spin states, D0 and D1. The potential energy surfaces are explored in an automated fashion using the global reaction route mapping strategy. The critical points and reaction paths have been fully optimized at the complete active space second order perturbation theory level taking all valence electrons in the active space.

Ab initio reaction pathways for photodissociation and isomerization of nitromethane on four singlet potential energy surfaces with three roaming paths.

Photodissociation pathways of nitromethane following π → π(*) electronic excitation are reported. The potential energy surfaces for four lowest singlet states are explored, and structures of many intermediates, dissociation limits, transition states, and minimum energy conical intersections were determined using the automated searching algorism called the global reaction route mapping strategy. Geometries are finally optimized at CASSCF(14e,11o) level and energies are computed at CAS(14o,11e)PT2 level.

Quantum mechanical fragment methods based on partitioning atoms or partitioning coordinates.

Conspectus The development of more efficient and more accurate ways to represent reactive potential energy surfaces is a requirement for extending the simulation of large systems to more complex systems, longer-time dynamical processes, and more complete statistical mechanical sampling. One way to treat large systems is by direct dynamics fragment methods. Another way is by fitting system-specific analytic potential energy functions with methods adapted to large systems.

Polarized Molecular Orbital Model Chemistry 3. The PMO Method Extended to Organic Chemistry.

The polarized molecular orbital (PMO) method, a neglect-of-diatomic-differential-overlap (NDDO) semiempirical molecular orbital method previously parameterized for systems composed of O and H, is here extended to carbon. We modified the formalism and optimized all the parameters in the PMO Hamiltonian by using a genetic algorithm and a database containing both electrostatic and energetic properties; the new parameter set is called PMO2. The quality of the resulting predictions is compared to results obtained by previous NDDO semiempirical molecular orbital methods, both including and excluding dispersion terms.

Valence excitation energies of alkenes, carbonyl compounds, and azabenzenes by time-dependent density functional theory: linear response of the ground state compared to collinear and noncollinear spin-flip TDDFT with the Tamm-Dancoff approximation.

Time-dependent density functional theory (TDDFT) holds great promise for studying photochemistry because of its affordable cost for large systems and for repeated calculations as required for direct dynamics. The chief obstacle is uncertain accuracy. There have been many validation studies, but there are also many formulations, and there have been few studies where several formulations were applied systematically to the same problems.

Electrostatically Embedded Molecular Tailoring Approach and Validation for Peptides.

We add higher-order electronic polarization effects to the molecular tailoring approach (MTA) by embedding each fragment in background charges as in combined quantum mechanical and molecular mechanical (QM/MM) methods; the resulting method considered here is called electrostatically embedded MTA (EE-MTA). We compare EE-MTA to MTA for a test peptide, Ace-(Ala)20-NMe, and we find that including background charges (embedding charges) greatly improves the performance. The fragmentation is performed on the basis of amino acids as monomers, and several sizes of fragment are tested.

Performance of recent and high-performance approximate density functionals for time-dependent density functional theory calculations of valence and Rydberg electronic transition energies.

We report a test of 30 density functionals, including several recent ones, for their predictions of 69 singlet-to-singlet excitation energies of 11 molecules. The reference values are experimental results collected by Caricato et al. for 30 valence excitations and 39 Rydberg excitations.

Assessment and validation of density functional approximations for iron carbide and iron carbide cation.

Using quantum chemical approximations to understand and predict complex transition metal chemistry, such as catalytic processes and materials properties, is an important activity in modern computational chemistry. High-level theory can sometimes provide high-precision benchmarks for systems containing transition metals, and these benchmarks can be used to understand the reliability of less expensive quantum chemical approximations that are applicable to complex systems. Here, we studied the ionization potential energy of Fe and FeC and the bond dissociation energies of FeC and FeC(+) by 15 density functional approximations: M05, M06, M06-L, ωB97, ωB97X, ωB97X-D, τ-HCTHhyb, BLYP, B3LYP, M08-HX, M08-SO, SOGGA11, SOGGA11-X, M11, and M11-L.

Incorporation of charge transfer into the explicit polarization fragment method by grand canonical density functional theory.

Molecular fragmentation algorithms provide a powerful approach to extending electronic structure methods to very large systems. Here we present a method for including charge transfer between molecular fragments in the explicit polarization (X-Pol) fragment method for calculating potential energy surfaces. In the conventional X-Pol method, the total charge of each fragment is preserved, and charge transfer between fragments is not allowed.

Polarizable Force Field for Protein with Charge Response Kernel.

We present a molecular mechanical force field for polypeptides and proteins involving the electronic polarization effect described with the charge response kernel. All of the electrostatic parameters for 20 amino acids are obtained by ab initio electronic structure calculations and combined with the AMBER99 force field. The refittings of dihedral angle parameters in the torsional potentials are performed so as to reproduce the ab initio optimized geometries and relative energies for the conformers of dipeptides.

Electronic polarization effect on low-frequency infrared and Raman spectra of aprotic solvent: molecular dynamics simulation study with charge response kernel by second order Møller-Plesset perturbation method.

Low-frequency infrared (IR) and depolarized Raman scattering (DRS) spectra of acetonitrile, methylene chloride, and acetone liquids are simulated via molecular dynamics calculations with the charge response kernel (CRK) model obtained at the second order Møller-Plesset perturbation (MP2) level. For this purpose, the analytical second derivative technique for the MP2 energy is employed to evaluate the CRK matrices. The calculated IR spectra reasonably agree with the experiments.