Accurate Quantum Chemical Reaction Energies for Lithium-Mediated Electrolyte Decomposition and Evaluation of Density Functional Approximations.

An important concern related to the performance of Li-ion batteries is the formation of a solid electrolyte interphase on the surface of the anode. This film is formed from the decomposition of electrolytes and can have important effects on the stability and performance. Here, we evaluate the decomposition pathway of ethylene carbonate and related organic electrolyte molecules using a series of density functional approximations and correlated wave function (WF) methods, including the coupled-cluster theory with single, double, and perturbative triple excitations [CCSD(T)] and auxiliary-field quantum Monte Carlo (AFQMC).

Multiple Stable Isoprene-Ozone Complexes Reveal Complex Entrance Channel Dynamics in the Isoprene + Ozone Reaction.

Accurately characterizing isoprene ozonolysis continues to challenge atmospheric chemists. The reaction is believed to be a spontaneous, concerted cycloaddition. However, little information is available about the entrance channel and isoprene-ozone complexes thought to define the long-range portion of the reaction coordinate.

Predicting Ligand-Dissociation Energies of 3d Coordination Complexes with Auxiliary-Field Quantum Monte Carlo.

Transition-metal complexes are ubiquitous in biology and chemical catalysis, yet they remain difficult to accurately describe with methods because of the presence of a large degree of dynamic electron correlation, and, in some cases, strong static correlation which results from a manifold of low-lying states. Progress has been hindered by a scarcity of high-quality gas-phase experimental data, while exact predictions are usually computationally unaffordable because of the large size of the relevant complexes. In this work, we present a data set of 34 tetrahedral, square planar, and octahedral 3d metal-containing complexes with gas-phase ligand-dissociation energies that have reported uncertainties of ≤2 kcal/mol.

Accurate Quantum Chemical Calculation of Ionization Potentials: Validation of the DFT-LOC Approach via a Large Data Set Obtained from Experiments and Benchmark Quantum Chemical Calculations.

Density functional theory (DFT) is known to often fail when calculating thermodynamic values, such as ionization potentials (IPs), due to nondynamical error (i.e., the self-interaction term).

Heterogenized Molecular Catalysts: Vibrational Sum-Frequency Spectroscopic, Electrochemical, and Theoretical Investigations.

Rhenium and manganese bipyridyl tricarbonyl complexes have attracted intense interest for their promising applications in photocatalytic and electrocatalytic CO reduction in both homogeneous and heterogenized systems. To date, there have been extensive studies on immobilizing Re catalysts on solid surfaces for higher catalytic efficiency, reduced catalyst loading, and convenient product separation. However, in order for the heterogenized molecular catalysts to achieve the combination of the best aspects of homogeneous and heterogeneous catalysts, it is essential to understand the fundamental physicochemical properties of such heterogeneous systems, such as surface-bound structures of Re/Mn catalysts, substrate-adsorbate interactions, and photoinduced or electric-field-induced effects on Re/Mn catalysts.

On Achieving High Accuracy in Quantum Chemical Calculations of 3 d Transition Metal-Containing Systems: A Comparison of Auxiliary-Field Quantum Monte Carlo with Coupled Cluster, Density Functional Theory, and Experiment for Diatomic Molecules.

The bond dissociation energies of a set of 44 3 d transition metal-containing diatomics are computed with phaseless auxiliary-field quantum Monte Carlo (ph-AFQMC) utilizing a correlated sampling technique. We investigate molecules with H, N, O, F, Cl, and S ligands, including those in the 3dMLBE20 database first compiled by Truhlar and co-workers with calculated and experimental values that have since been revised by various groups. In order to make a direct comparison of the accuracy of our ph-AFQMC calculations with previously published results from 10 DFT functionals, CCSD(T), and icMR-CCSD(T), we establish an objective selection protocol which utilizes the most recent experimental results except for a few cases with well-specified discrepancies.

Collaboration between experiment and theory in solar fuels research.

As the challenges in science increase in scope and interdisciplinarity, collaboration becomes increasingly important. Our groups have maintained close collaborations for solar fuels research over the past decade. Based on this experience, we discuss strategies for collaboration between experiment and theory including facilitation of effective communication and navigation of problems that arise.

Inverse Design of a Catalyst for Aqueous CO/CO Conversion Informed by the Ni-Iminothiolate Complex.

A computational inverse design method suitable to assist the development and optimization of molecular catalysts is introduced. Catalysts are obtained by continuous optimization of "alchemical" candidates in the vicinity of a reference catalyst with well-defined reaction intermediates and rate-limiting step. A Ni-iminoalkoxylate catalyst for aqueous CO/CO conversion is found with improved performance relative to a Ni-iminothiolate reference complex, previously reported as a biomimetic synthetic model of CO dehydroxygenase.

CO Reduction Catalysts on Gold Electrode Surfaces Influenced by Large Electric Fields.

Attaching molecular catalysts to metal and semiconductor electrodes is a promising approach to developing new catalytic electrodes with combined advantages of molecular and heterogeneous catalysts. However, the effect of the interfacial electric field on the stability, activity, and selectivity of the catalysts is often poorly understood due to the complexity of interfaces. In this work, we examine the strength of the interfacial field at the binding site of CO reduction catalysts including Re(S-2,2'-bipyridine)(CO)Cl and Mn(S-2,2'-bipyridine)(CO)Br immobilized on Au electrodes.

Electron-Hole-Pair-Induced Vibrational Energy Relaxation of Rhenium Catalysts on Gold Surfaces.

A combination of time-resolved vibrational spectroscopy and density functional theory techniques have been applied to study the vibrational energy relaxation dynamics of the Re(4,4'-dicyano-2,2'-bipyridine)(CO)Cl (Re(CO)Cl) catalyst for CO to CO conversion bound to gold surfaces. The kinetics of vibrational relaxation exhibits a biexponential decay including an ultrafast initial relaxation and complete recovery of the ground vibrational state. Ab initio molecular dynamics simulations and time-dependent perturbation theory reveal the former to be due to vibrational population exchange between CO stretching modes and the latter to be a combination of intramolecular vibrational relaxation (IVR) and electron-hole pair (EHP)-induced energy transfer into the gold substrate.

Thousandfold Enhancement of Photoreduction Lifetime in Re(bpy)(CO) via Spin-Dependent Electron Transfer from a Perylenediimide Radical Anion Donor.

Spin-dependent intramolecular electron transfer is revealed in the Re(CO)(py)(bpy-Ph)-perylenediimide radical anion (Re-bpy-PDI) dyad, a prototype model system for artificial photosynthesis. Quantum chemical calculations and ultrafast transient absorption spectroscopy experiments demonstrate that selective photoexcitation of Re-bpy results in electron transfer from PDI to Re-bpy, forming two distinct charge-shifted states. One is an overall doublet whose return to the ground state is spin-allowed.

Photoinduced electron transfer from rylenediimide radical anions and dianions to Re(bpy)(CO) using red and near-infrared light.

A major goal of artificial photosynthesis research is photosensitizing highly reducing metal centers using as much as possible of the solar spectrum reaching Earth's surface. The radical anions and dianions of rylenediimide (RDI) dyes, which absorb at wavelengths as long as 950 nm, are powerful photoreductants with excited state oxidation potentials that rival or exceed those of organometallic chromophores. These dyes have been previously incorporated into all-organic donor-acceptor systems, but have not yet been shown to reduce organometallic centers.

A full set of iridium(iv) pyridine-alkoxide stereoisomers: highly geometry-dependent redox properties.

We introduce and characterize the complete set of possible isomers of Ir(pyalk)Cl (pyalk = 2-(pyridin-2-yl)propan-2-oate), providing valuable insights on the properties of Ir(iv) species. The pyridine alkoxide ligand strongly stabilizes high oxidation states, essential to accessing the catalytically relevant Ir(iv) state, and results in robust complexes that can be handled under ambient conditions, even permitting chromatographic separation. The redox properties are isomer-dependent, spanning a 300 mV range, rationalized with ligand-field theory and DFT calculations.

Computed Regioselectivity and Conjectured Biological Activity of Ene Reactions of Singlet Oxygen with the Natural Product Hyperforin.

Hyperforin is a constituent of St. John's wort and coexists with the singlet oxygen sensitizer hypericin. Density functional theory, molecular mechanics and Connolly surface calculations show that accessibility in the singlet oxygen "ene" reaction favors the hyperforin "southwest" and "southeast" prenyl (2-methyl-2-butenyl) groups over the northern prenyl groups.

Fundamental Role of Oxygen Stoichiometry in Controlling the Band Gap and Reactivity of Cupric Oxide Nanosheets.

CuO is a nonhazardous, earth-abundant material that has exciting potential for use in solar cells, photocatalysis, and other optoelectronic applications. While progress has been made on the characterization of properties and reactivity of CuO, there remains significant controversy on how to control the precise band gap by tuning conditions of synthetic methods. Here, we combine experimental and theoretical methods to address the origin of the wide distribution of reported band gaps for CuO nanosheets.

Molecular titanium-hydroxamate complexes as models for TiO2 surface binding.

Hydroxamate binding modes and protonation states have yet to be conclusively determined. Molecular titanium(iv) phenylhydroxamate complexes were synthesized as structural and spectroscopic models, and compared to functionalized TiO2 nanoparticles. In a combined experimental-theoretical study, we find that the predominant binding form is monodeprotonated, with evidence for the chelate mode.

Ultrafast Photoinduced Interfacial Proton Coupled Electron Transfer from CdSe Quantum Dots to 4,4'-Bipyridine.

Pyridine and derivatives have been reported as efficient and selective catalysts for the electrochemical and photoelectrochemical reduction of CO2 to methanol. Although the catalytic mechanism remains a subject of considerable recent debate, most proposed models involve interfacial proton coupled electron transfer (PCET) to electrode-bound catalysts. We report a combined experimental and theoretical study of the photoreduction of 4,4'-bipyridium (bPYD) using CdSe quantum dots (QDs) as a model system for interfacial PCET.

Assessment of DFT for Computing Sum Frequency Generation Spectra of an Epoxydiol and a Deuterated Isotopologue at Fused Silica/Vapor Interfaces.

We assess the capabilities of eight popular density functional theory (DFT) functionals, in combination with several basis sets, as applied to calculations of vibrational sum frequency generation (SFG) spectra of the atmospherically relevant isoprene oxidation product trans-β-isoprene epoxydiol (IEPOX) and one of its deuterated isotopologues at the fused silica/vapor interface. We use sum of squared differences (SSD) and total absolute error (TAE) calculations to estimate the performance of each functional/basis set combination in producing SFG spectra that match experimentally obtained spectra from trans-β-IEPOX and one of its isotopologues. Our joined SSD/TAE analysis shows that while the twist angle of the methyl C3v symmetry axis of trans-β-IEPOX relative to the surface is sensitive to the choice of DFT functional, the calculated tilt angle relative to the surface normal is largely independent of the functional and basis set.

Stable Iridium(IV) Complexes of an Oxidation-Resistant Pyridine-Alkoxide Ligand: Highly Divergent Redox Properties Depending on the Isomeric Form Adopted.

The preparation of the facial and meridional isomers of [Ir(pyalk)3] (pyalk = 2-(2-pyridyl)isopropanoate), as model complexes for a powerful water oxidation catalyst, is reported. The strongly donating N3O3 ligand set is very oxidation-resistant, yet promotes facile metal-centered oxidation to form stable Ir(IV) compounds. The Ir(III/IV) reduction potentials of the two isomers differ by 340 mV despite the identical ligand set.

Facet-dependent photoelectrochemical performance of TiO2 nanostructures: an experimental and computational study.

The behavior of crystalline nanoparticles depends strongly on which facets are exposed. Some facets are more active than others, but it is difficult to selectively isolate particular facets. This study provides fundamental insights into photocatalytic and photoelectrochemical performance of three types of TiO(2) nanoparticles with predominantly exposed {101}, {010}, or {001} facets, where 86-99% of the surface area is the desired facet.

Theoretical study of the reaction formalhydrazone with singlet oxygen. Fragmentation of the C=N bond, ene reaction and other processes.

Photobiologic and synthetic versatility of hydrazones has not yet been established with (1)O2 as a route to commonly encountered nitrosamines. Thus, to determine whether the "parent" reaction of formalhydrazone and (1)O2 leads to facile C=N bond cleavage and resulting nitrosamine formation, we have carried out CCSD(T)//DFT calculations and analyzed the energetics of the oxidation pathways. A [2 + 2] pathway occurs via diradicals and formation of 3-amino-1,2,3-dioxazetidine in a 16 kcal/mol(-1) process.