: The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg

Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields

This perspective article outlines a simple but general theoretical analysis for multiple proton–electron transfer reactions, based on the microscopic theory of proton-coupled electron transfer reactions, recent developments in the thermodynamic theory of multi-step electron transfer reactions, and the experimental realization that many multiple proton-coupled electron transfer reactions feature decoupled proton–electron steps in their mechanism It is shown that decoupling of proton and electron transfer leads to a strong pH dependence of the overall catalytic reaction, implying an optimal pH for high catalytic turnover, and an associated optimal catalyst at the optimal pH When more than one catalytic intermediate is involved, scaling relationships between intermediates may dictate the optimal catalyst and limit the extent of reversibility that may be achievable for a multiple proton–electron transfer reaction The theory is discussed in relation to the experimental results for a number of redox reactions that are of importance for sustainable energy conversion, primarily focusing on their pH dependence

/pdf/theory-of-multiple-proton-electron-transfer-reactions-and-1ihrjykiv5.pdf

Theory of multiple proton–electron transfer reactions and its implications for electrocatalysis

This paper presents a review of the redox and electrocatalytic properties of transition metal oxide electrodes, paying particular attention to the oxygen evolution reaction. Metal oxide materials may be prepared using a variety of methods, resulting in a diverse range of redox and electrocatalytic properties. Here we describe the most common synthetic routes and the important factors relevant to their preparation. The redox and electrocatalytic properties of the resulting oxide layers are ascribed to the presence of extended networks of hydrated surface bound oxymetal complexes termed surfaquo groups. This interpretation presents a possible unifying concept in water oxidation catalysis – bridging the fields of heterogeneous electrocatalysis and homogeneous molecular catalysis.

/pdf/redox-and-electrochemical-water-splitting-catalytic-gu7vfe19dz.pdf

Redox and electrochemical water splitting catalytic properties of hydrated metal oxide modified electrodes

In our previous work [J. Chem. Theory Comput. 2013, 9, 4959], we introduced the PYXAID program, developed for the purpose of performing nonadiabatic molecular dynamics simulations in large-scale condensed matter systems. The methodological aspects and the basic capabilities of the program have been extensively discussed. In the present work, we perform a thorough investigation of advanced capabilities of the program, namely, the advanced integration techniques for the time-dependent Schrodinger equation (TD-SE), the decoherence corrections via decoherence-induced surface hopping, the use of multiexciton basis configurations, and the direct simulation of photoexcitation via explicit light–matter interaction. We demonstrate the importance of the mentioned features by studying the electronic dynamics in a variety of systems. In particular, we demonstrate that the advanced integration techniques for solving TD-SE may lead to a significant speedup of the calculations and provide more stable solutions. We show ...

Advanced Capabilities of the PYXAID Program: Integration Schemes, Decoherence Effects, Multiexcitonic States, and Field-Matter Interaction

Molecular electrocatalysts can play an important role in energy storage and utilization reactions needed for intermittent renewable energy sources. This manuscript describes three general themes that our laboratories have found useful in the development of molecular electrocatalysts for reduction of CO2 to CO and for H2 oxidation and production. The first theme involves a conceptual partitioning of catalysts into first, second, and outer coordination spheres. This is illustrated with the design of electrocatalysts for CO2 reduction to CO using first and second coordination spheres and for H2 production catalysts using all three coordination spheres. The second theme focuses on the development of thermodynamic models that can be used to design catalysts to avoid high- and low-energy intermediates. In this research, new approaches to the measurement of thermodynamic hydride donor and acceptor abilities of transition-metal complexes were developed. Combining this information with other thermodynamic informat...

Development of molecular electrocatalysts for energy storage.

Domen has observed that the GaN/ZnO semiconductor alloy serves, in the presence of a sacrificial electron scavenger, as a photocatalyst for solar water oxidation, producing H+ and O2 at the aqueous/semiconductor interface. With a suitable cocatalyst, the same solar photoexcitation process also generates H2 from H+. The active sites, mechanisms, and reaction intermediates are not known. This paper describes atomistic modeling and proposes a sequence of intermediate steps for the water oxidation process at a pure GaN/water interface. Pure GaN is known to be photocatalytically active but only in the UV region, because the semiconductor band gap is 3.4 eV, outside the visible region of the spectrum. However, it serves as an appropriate model system in the absence of more detailed information. A flat (1010) nonpolar surface is chosen to model an active site. Ab initio molecular dynamics simulations examine the fully solvated aqueous interface at ambient temperature. An appropriate cluster model, that includes...

Photocatalytic Water Oxidation at the GaN (101̄0)-Water Interface

The properties of the hydrogenase-inspired [Ni(PNP)2]2+ (PNP = Et2PCH2NMeCH2PEt2) catalyst for homogeneous hydrogen oxidation in acetonitrile solution are explored from a theoretical perspective for hydrogen production. The defining characteristic of this catalyst is the presence of pendent bases in the second coordination sphere that function as proton relays between the solution and the metal center. DFT calculations of the possible intermediates along proposed catalytic pathways are carried out and used to construct coupled Pourbaix diagrams of the redox processes and free-energy profiles along the reaction pathways. Analysis of the coupled Pourbaix diagrams reveals insights into the intermediate species and the mechanisms favored at different pH values of the solution. Consideration of the acid–base behavior of the metal hydride and H2 adduct species imposes additional constraints on the reaction mechanism, which can involve intramolecular as well as intermolecular proton-coupled electron-transfer steps. The efficacy of the catalyst is shown to depend critically on the pKa values of these potential intermediates, as they control both the species in solution at a given pH and the free-energy profile of reaction pathways. Optimal relationships among these pKa values can be identified, and it is demonstrated that “proton management”, i.e., the manipulation of these pKa values (e.g., through choice of metal or substituents on ligands), can serve as a design principle for improved catalytic behavior.

/pdf/proton-management-as-a-design-principle-for-hydrogenase-16h33l1zfp.pdf

Proton management as a design principle for hydrogenase-inspired catalysts

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Photocatalytic Water Oxidation at the GaN (101̄0)-Water Interface

Proton management as a design principle for hydrogenase-inspired catalysts