Showing papers in "Journal of Physical Chemistry A in 2019"
TL;DR: With the new parametrization, same-spin correlation can be eliminated at minimal cost in performance, which permits revD OD-PBEP86-D4 and revDOD-PBE-D 4 functionals that scale as N4 or even N3 with the size of the system, and the very recent D4 dispersion correction is clearly superior over D3(BJ.
Abstract: We present a family of minimally empirical double-hybrid DFT functionals parametrized against the very large and diverse GMTKN55 benchmark. The very recently proposed ωB97M(2) empirical double hybrid (with 16 adjustable parameters) has the lowest WTMAD2 (weighted mean absolute deviation over GMTKN55) ever reported at 2.19 kcal/mol. However, refits of the DSD-BLYP and DSD-PBEP86 spin-component-scaled, dispersion-corrected double hybrids can achieve WTMAD2 values as low as 2.33 with the very recent D4 dispersion correction (2.42 kcal/mol with the D3(BJ) dispersion term) using just a handful of adjustable parameters. If we use full DFT correlation in the initial orbital evaluation, the xrevDSD-PBEP86-D4 functional reaches WTMAD2 = 2.23 kcal/mol, statistically indistinguishable from ωB97M(2) but using just four nonarbitrary adjustable parameters (and three semiarbitrary ones). The changes from the original DSD parametrizations are primarily due to noncovalent interaction energies for large systems, which were undersampled in the original parametrization set. With the new parametrization, same-spin correlation can be eliminated at minimal cost in performance, which permits revDOD-PBEP86-D4 and revDOD-PBE-D4 functionals that scale as N4 or even N3 with the size of the system. Dependence of WTMAD2 for DSD functionals on the percentage of HF exchange is roughly quadratic; it is sufficiently weak that any reasonable value in the 64% to 72% range can be chosen semiarbitrarily. DSD-SCAN and DOD-SCAN double hybrids involving the SCAN nonempirical meta-GGA as the semilocal component have also been considered and offer a good alternative if one wishes to eliminate either the empirical dispersion correction or the same-spin correlation component. noDispSD-SCAN66 achieves WTMAD2 = 3.0 kcal/mol, compared to 2.7 kcal/mol for DOD-SCAN66-D4. However, the best performance without dispersion corrections (WTMAD2 = 2.8 kcal/mol) is reached by revωB97X-2, a slight reparametrization of the Chai-Head-Gordon range-separated double hybrid. Finally, in the context of double-hybrid functionals, the very recent D4 dispersion correction is clearly superior over D3(BJ).
216 citations
TL;DR: The different algorithmic approaches for the investigation of chemical reaction networks differ in their application range, the level of completeness of the exploration, and the amount of heuristics and human intervention required.
Abstract: For the investigation of chemical reaction networks, the identification of all relevant intermediates and elementary reactions is mandatory. Many algorithmic approaches exist that perform explorations efficiently and in an automated fashion. These approaches differ in their application range, the level of completeness of the exploration, and the amount of heuristics and human intervention required. Here, we describe and compare the different approaches based on these criteria. Future directions leveraging the strengths of chemical heuristics, human interaction, and physical rigor are discussed.
145 citations
TL;DR: This work reoptimizes the range-separated hybrid meta functional M11 to obtain a new functional called revM11 that gives good performance for all three types of electronic excitations and at the same time gives very good predictions across-state properties.
Abstract: The ability of Kohn–Sham density functional theory (KS-DFT) to accurately predict various types of electronic excitation energies with (necessarily approximate) exchange-correlation functionals faces several challenges. Chief among these is that valence excitations are usually inherently multiconfigurational and therefore best treated by functionals with local exchange, whereas Rydberg and charge-transfer excitations are often better treated with nonlocal exchange. The question arises regarding whether one can optimize a functional such that all three kinds of excitations (valence, Rydberg, and charge transfer, including long-range charge transfer) are treated in a balanced and accurate way. The goal of the present work is to try to answer that question and then to optimize a functional with the best possible balanced behavior. Of the variety of functional types available, we choose to use a range-separated hybrid meta functional for the following reasons: (i) Range separation allows the percentage of Har...
72 citations
TL;DR: These reaction rate coefficients are sufficiently large that unimolecular chemistry is the dominant fate of these monoterpene-derived RO2 in the atmosphere.
Abstract: Atmospheric oxidation of monoterpenes (emitted primarily by evergreen trees) is known to contribute to the formation and growth of aerosol particles. While recent research has tied the formation of organic aerosol to unimolecular chemistry of the organic peroxy radicals (RO2) formed in the oxidation of monoterpenes, the fundamental physical chemistry of these RO2 remains obscure. Here we use isomer-specific measurements and ab initio calculations to determine the unimolecular reaction rates and products of RO2 derived from the hydroxyl radical (OH) oxidation of α-pinene and β-pinene. Among all of the structural isomers of the first-generation RO2 from both monoterpenes, we find that the first-generation RO2 produced following opening of the four-membered ring undergo fast unimolecular reactions (4 ± 2 and 16 ± 5 s–1 for α-pinene and β-pinene, respectively) at 296 K, in agreement with high-level ab initio calculations. The presence of the hydroxy group and carbon–carbon double bond in the ring-opened RO2 e...
71 citations
TL;DR: An alternative response function, based on the dual descriptor in terms of Koopmans' approximation, is proposed for the description of chemical reactivity in systems with (quasi-) degenerate frontier molecular orbitals, and has proven to accurately describe the chemical reactsivity and aromaticity of the studied systems.
Abstract: An alternative response function, based on the dual descriptor in terms of Koopmans' approximation, is hereby proposed for the description of chemical reactivity in systems with (quasi-) degenerate frontier molecular orbitals. This descriptor is constructed from Fukui functions that include contributions from different orbitals, i.e., orbital-weighted Fukui functions. The methodology is applied to three case studies: the first case consists of a series of benchmark organic and inorganic molecules from which the dual descriptor, based only on frontier orbitals, is not appropriate to describe their reactivity. The second case deals with the proper description of chemical reactivity in Diels-Alder reactions between fullerene C60 and cyclopentadiene (CP), revealing the importance of considering secondary orbital interactions for an adequate regioselectivity description. The third, and last case, consists of a series of polycyclic aromatic hydrocarbons (PAHs) possessing molecular orbital degeneracy. By means of analyzing of this descriptor, an alternative approach to the description of aromaticity is proposed. In all cases, the proposed index called "orbital-weighted dual descriptor" has proven to accurately describe the chemical reactivity and aromaticity of the studied systems.
66 citations
TL;DR: This appears to be the first example of a stable closed-shell organic molecule exhibiting S1/T1 inversion at its equilibrium geometry and has profound implications for organic optoelectronics as well as for water-splitting photocatalysis with heptazine-based polymers which have yet to be systematically explored and exploited.
Abstract: According to Hund’s rule, the lowest triplet state (T1) is lower in energy than the lowest excited singlet state (S1) in closed-shell molecules. The exchange integral lowers the energy of the tripl...
65 citations
TL;DR: Quantitative analysis shows that NN learning is sensitive to the data set used for training, and results show that user-sampled structures obtained with the quantum chemical iMD-VR machinery enable excellent sampling in the vicinity of the minimum energy path (MEP).
Abstract: While the primary bottleneck to a number of computational workflows was not so long ago limited by processing power, the rise of machine learning technologies has resulted in an interesting paradig...
64 citations
TL;DR: A methodology for graph based enumeration of surfaces and unique chemical adsorption structures bonded to those surfaces is presented and a unique graph representation for any general slab cleave is created and extended to include a large variety of catalytically relevant adsorbed molecules.
Abstract: We present a methodology for graph based enumeration of surfaces and unique chemical adsorption structures bonded to those surfaces. Utilizing the graph produced from a bulk structure, we create a unique graph representation for any general slab cleave and further extend that representation to include a large variety of catalytically relevant adsorbed molecules. We also demonstrate simple geometric procedures to generate 3D initial guesses of these enumerated structures. While generally useful for generating a wide variety of structures used in computational surface science and heterogeneous catalysis, these techniques are also key to facilitating an informatics approach to the high-throughput search for more effective catalysts.
64 citations
TL;DR: This work adopts a transfer learning technique to train neural network models that achieve good performance even with a relatively small set of high-accuracy data, and develops thermochemistry predictors for organic compounds with oxygen and nitrogen heteroatoms that approach experimental and coupled cluster accuracy while only requiring molecular graph inputs.
Abstract: Machine learning provides promising new methods for accurate yet rapid prediction of molecular properties, including thermochemistry, which is an integral component of many computer simulations, particularly automated reaction mechanism generation. Often, very large data sets with tens of thousands of molecules are required for training the models, but most data sets of experimental or high-accuracy quantum mechanical quality are much smaller. To overcome these limitations, we calculate new high-level data sets and derive bond additivity corrections to significantly improve enthalpies of formation. We adopt a transfer learning technique to train neural network models that achieve good performance even with a relatively small set of high-accuracy data. The training data for the entropy model are carefully selected so that important conformational effects are captured. The resulting models are generally applicable thermochemistry predictors for organic compounds with oxygen and nitrogen heteroatoms that approach experimental and coupled cluster accuracy while only requiring molecular graph inputs. Due to their versatility and the ease of adding new training data, they are poised to replace conventional estimation methods for thermochemical parameters in reaction mechanism generation. Since high-accuracy data are often sparse, similar transfer learning approaches are expected to be useful for estimating many other molecular properties.
63 citations
TL;DR: The authors have shown that phase transitions of aerosol particles are sensitive to pH, focusing on systems that undergo liquid-liquid phase separation.
Abstract: pH is one of the most basic chemical properties of aqueous solution, but its measurement in nanoscale aerosol particles presents many challenges. The pH of aerosol particles is of growing interest in the atmospheric chemistry community because of its demonstrated effects on heterogeneous chemistry and human health, as well as potential effects on climate. The authors have shown that phase transitions of aerosol particles are sensitive to pH, focusing on systems that undergo liquid–liquid phase separation. Currently, aerosol pH is calculated indirectly from knowledge of species present in the gas and aerosol phases through the use of thermodynamic models. From these models, ambient aerosol is expected to be highly acidic (pH ∼ 0–3). Direct measurements have focused on model systems due to the difficulty of this measurement. This area is one in which physical chemists should be encouraged to contribute because of the potential consequences for aerosol processes in the environment.
63 citations
TL;DR: This work studies the dynamics of molecular vibrational polaritons in various solvent environments and proposes the intermediate state to be the high-lying excited states of dark modes, which are effectively populated by LP via, e.g., ladder-climbing.
Abstract: The modification of vibrational dynamics is essential for controlling chemical reactions and IR photonic applications. The hybridization between cavity modes and molecular vibrational modes provide...
TL;DR: Using a high-level multiconformer transition state theory (MC-TST) approach, recommended temperature dependent reaction rate coefficients for a number of the H-shift reactions in the isoprene oxidation mechanism are determined and it is found that most of the aldehydic and α-hydroxy H-shifts have rate constants that make them competitive with bimolecular reactions inThe atmosphere under typical atmospheric conditions.
Abstract: With an annual emission of about 500 Tg, isoprene is an important molecule in the atmosphere. While much of its chemistry is well constrained by either experiment or theory, the rates of many of the unimolecular peroxy radical hydrogen-shift (H-shift) reactions remain speculative. Using a high-level multiconformer transition state theory (MC-TST) approach, we determine recommended temperature dependent reaction rate coefficients for a number of the H-shift reactions in the isoprene oxidation mechanism. We find that most of the (1,4, 1,5, and 1,6) aldehydic and (1,5 and 1,6) α-hydroxy H-shifts have rate constants at 298.15 K in the range 10–2 to 1 s–1, which make them competitive with bimolecular reactions in the atmosphere under typical atmospheric conditions. In addition, we find that the rate coefficients of different diastereomers can differ by up to 3 orders of magnitude, illustrating the importance of chirality. Implementation of our calculated reaction rate coefficients into the most recent GEOS-Che...
TL;DR: This work investigates here how collective coupling effects modify the mechanisms and rates of photochemical processes, in particular, photodissociation and non-radiative decay in NaI and pyrazine, respectively, through the coupling of a molecular ensemble to the confined electromagnetic modes of a microcavity.
Abstract: The coupling of a molecular ensemble to the confined electromagnetic modes of a microcavity can strongly modify the photophysics and photochemistry of the molecules upon photoexcitation. We investi...
TL;DR: It was found that the use of the proposed descriptors significantly improves the accuracy of the machine learning algorithm, particularly at low pressures, compared to the predictions made based solely on the rest structural features.
Abstract: In the present study, we propose a new set of descriptors that, along with a few structural features of nanoporous materials, can be used by machine learning algorithms for accurate predictions of ...
TL;DR: New approaches that apply the fluctuation theory of statistical mechanics to dynamics enable the direct determination of the activation energy for an arbitrary dynamical time scale from simulations at a single temperature, promising important new mechanistic information for a broad range of chemical processes.
Abstract: Recent advances in the calculation and interpretation of the activation energy for a dynamical process are described. Specifically, new approaches that apply the fluctuation theory of statistical m...
TL;DR: Using quantum chemistry, this work provides a molecular-level explanation for the synergistic effects in sulfuric acid-dimethylamine-ammonia cluster formation and shows that ammonia can increase the particle formation rate by up to 5 orders of magnitude compared to the two-component sulfuric Acid-amine system.
Abstract: The abundance and basicity of a stabilizing base have shown to be key factors in sulfuric acid driven atmospheric new-particle formation. However, since experiments indicate that a low concentration of ammonia enhances particle formation from sulfuric acid and dimethylamine, which is a stronger base, there must be additional factors affecting the particle formation efficiency. Using quantum chemistry, we provide a molecular-level explanation for the synergistic effects in sulfuric acid-dimethylamine-ammonia cluster formation. Because of the capability of ammonia to form more intermolecular interactions than dimethylamine, it can act as a bridge-former in sulfuric acid-dimethylamine clusters. In many cluster compositions, ammonia is more likely to be protonated than dimethylamine, although it is a weaker base. By nanoparticle formation rate simulations, we show that due to the synergistic effects, ammonia can increase the particle formation rate by up to 5 orders of magnitude compared to the two-component sulfuric acid-amine system.
TL;DR: A reasonable correlation between the observed and the DFT-predicted results is established and insights into the electronic structure of the ILs are given.
Abstract: The effect of the anion size and electronegativity of halide-based anions (Cl-, Br-, I-, and BF4-) on the interionic interaction in 1-ethyl-3-methylimidazolium-based ionic liquids (ILs) C2mim X (X = Cl, Br, I, and BF4) is studied by a combined approach of experiments (Raman, IR, UV-vis spectroscopy) and quantum chemical calculations. The fingerprint region of the Raman spectra of these C2mim X ion-pairs provides evidence of the presence of the conformational isomerism in the alkyl chain of the C2mim+ cation. The Raman and IR bands of the imidazolium C2-H stretch vibration for C2mim X (X = Cl, Br, I, and BF4) were noticeably blue-shifted with the systematic change in size of anions and the electronegativity. The observed blue shift in the C2-H stretch vibration follows the order C2mim BF4 > C2mim I > C2mim Br > C2mim Cl, which essentially indicates the strong hydrogen bonding in the C2mim Cl ion-pair. DFT calculations predict at least four configurations for the cation-anion interaction. On the basis of relative optimized energies and basis-set-superposition-error (BSSE) corrected binding energies for all ion-pair configurations, the most active site for the anion interaction was found at the C2H position of the cation. Besides information about the C2H position, our DFT results give insights into the anion interaction with the ethyl and methyl chain of the cation, which was also confirmed experimentally [ Chem. Commun. 2015 , 51 , 3193 ]. The anion interaction at the C2H site of the cation favors a planar geometry in C2mim X for X = Cl, Br, and I; however, for BF4, the system prefers a nonplanar geometry where the anion is located over the imidazolium ring. TD-DFT results were used to analyze the observed UV-vis absorption spectra in a more adequate way giving insights into the electronic structure of the ILs. Overall, a reasonable correlation between the observed and the DFT-predicted results is established.
TL;DR: The current Feature Article analyzes aspects of confinement with a special emphasis on the work done by the research group, thereby affecting its reactivity as well as various response properties as compared to the cases of corresponding unconfined systems.
Abstract: Confined systems often exhibit unusual behavior regarding their structure, stability, reactivity, bonding, interactions, and dynamics. Quantization is a direct consequence of confinement. Confinement modifies the electronic energy levels, orbitals, electronic shell filling, etc. of a system, thereby affecting its reactivity as well as various response properties as compared to the cases of corresponding unconfined systems. Confinement may force two rare gas atoms to form a partly covalent bond. Gas storage is facilitated through confinement and unprecedented optoelectronic properties are observed in certain cases. Some slow reactions get highly accelerated in an appropriate confined environment. In the current Feature Article we analyze these aspects with a special emphasis on the work done by our research group.
TL;DR: Possible approaches to searching for optimal configurations and one alternative based on systematic configurational sampling, which seems able to overcome the typical problems associated with searching for global minima on multidimensional potential energy surfaces are discussed.
Abstract: We studied the configurational sampling of noncovalently bonded molecular clusters relevant to the atmosphere. In this article, we discuss possible approaches to searching for optimal configuration...
TL;DR: Recent advances in the fundamental understandings of catalytic CO oxidation by O2 mediated with heteronuclear metal oxide clusters (HMOCs) are presented and discussed using state-of-the-art mass spectrometry and quantum chemistry calculations.
Abstract: Oxidation of CO into CO2 is a prototypical reaction in heterogeneous catalysis and is one of the extensively studied reactions in the gas phase to explore the underlying mechanisms of related catalysis. In this Feature Article, we present and discuss our recent advances in the fundamental understanding of catalytic CO oxidation by O2 mediated with heteronuclear metal oxide clusters (HMOCs) using state-of-the-art mass spectrometry and quantum chemistry calculations. The HMOCs can be considered as ideal models for active sites on mixed or oxide supported catalysts at a strictly molecular level. A concept of electronegativity-ladder effect was proposed to account for the enhanced reactivity of noble metal (NM) doped HMOCs, and then this effect was successfully extended in the design of NM-free HMOCs in catalytic CO oxidation by O2. The future directions and the challenges were also discussed.
TL;DR: The spin-orbit coupling constants (SOCC) in atoms and ions of the first- through third-row transition elements were calculated for the low-lying atomic states whose main electron configuration is [ nd] q, suggesting that the LS-coupling scheme is inappropriate.
Abstract: The spin-orbit coupling constants (SOCC) in atoms and ions of the first- through third-row transition elements were calculated for the low-lying atomic states whose main electron configuration is [ nd] q ( q = 1-4 and 6-9, n = the principal quantum number), using four different approaches: (1) a nonrelativistic Hamiltonian used to construct multiconfiguration self-consistent field (MCSCF) wave functions utilizing effective core potentials and their associated basis sets within the framework of second-order configuration interaction (SOCI) to calculate spin-orbit couplings (SOC) using one-electron Breit-Pauli Hamiltonian (BPH), (2) a nonrelativistic Hamiltonian used to construct MCSCF wave functions utilizing model core potentials and their associated basis sets within the framework of SOCI to calculate SOC using the full BPH, (3) nonrelativistic and spin-independent relativistic Hamiltonians used to construct MCSCF wave functions utilizing all-electron (AE) basis sets within the framework of SOCI to calculate SOC using the full BPH, and (4) a relativistic Hamiltonian given by the exact two-component (X2C) transformation for construction of Kramers-restricted relativistic configuration interaction wave functions. In this investigation, these four approaches are referred to as ECP, MCP, AE, and X2C methods, respectively. The ECP, MCP, and AE methods are so-called two-step approaches (TSA), while the X2C method is a one-step approach (OSA). In the AE method, three different calculations-relativistic elimination of small components (RESC), third-order Douglas-Kroll-Hess (DKH3), and infinite-order two-component (IOTC) relativistic correction-were performed for the estimation of the scalar relativistic components in addition to those of the nonscalar relativistic (NSR) contributions. The calculated SOCC are compared to the available experimental data via the Lande interval rule. Although there are several exceptions, including states whose main configuration is [ nd]5, the average differences between the ECP and AE (IOTC) SOCC and between the ECP and the X2C SOCC are mostly less than 20%. The differences between the ECP and the experimental SOCC are even smaller. No serious discrepancy was found between the TSA and OSA predictions of SOCC for the first- and second-row transition elements in comparison to experiment. For atoms and ions of the third-row transition elements, the SOCC calculated through the Lande interval rule are not reliable. The low-energy spin-mixed (SM) states originating from a [5d] q configuration ( q = 2-4) have a larger energy lowering due to the SOC effects, in comparison with those for atoms and ions of the first- and second-row transition elements. For the spin-mixed (SM) states originating from a [5d] q configuration ( q = 6-8), the energy lowering of all 4F7/2, 5D1, and 5D3 states due to the SOC effects is smaller than those of the other SM states. This difficulty, which also arises for the MCP, AE, and X2C (OSA) approaches, suggests that the LS-coupling scheme is inappropriate.
TL;DR: In this article, the authors proposed visualized methods to investigate the physical mechanism of a chiral molecule, where the electric and magnetic interactions are visualized with the transitional electric dipole moments, the transitional magnetic dipole moment, and the transition electric quadrupole moment and their tensor product.
Abstract: The chiral source and its mechanism in the molecular system are of great significance in many fields. In this work, we proposed visualized methods to investigate the physical mechanism of a chiral molecule, where the electric and magnetic interactions are visualized with the transitional electric dipole moment, the transitional magnetic dipole moment, and the transitional electric quadrupole moment, and their tensor product. This will also serve as an effective means of visualizing the interaction of light with matter. The relationship between the molecular Raman optical activity (ROA) response and molecular structure was analyzed in an intuitive way. The relationship between chromophore chirality and molecular vibration mode are revealed via interaction between the transition electric dipole moment and the transition magnetic dipole moment. The molecular chirality is derived from the anisotropy of the molecular transition electric dipole moment and the transition magnetic dipole moment. The anisotropic dipole moment localized molecular chromophore is the source of the vibration mode in which the ROA responds to the reverse.
TL;DR: This work systematically investigated the generality of the ML models, the choice of features and target labels, and the distance and orientation dependence of electronic coupling, and developed a machine learning approach to evaluate electronic coupling.
Abstract: Electron transfer coupling is a critical factor in determining electron transfer rates. This coupling strength can be sensitive to details in molecular geometries, especially intermolecular configu...
TL;DR: It is found that a model originally trained on hydrocarbons and oxygenates can broaden its prediction coverage to nitrogen-containing species via an active learning process, suggesting that the continuous learning strategy is not only able to improve the model accuracy but is also capable of expanding the predictive capacity of a model to unseen species domains.
Abstract: Because collecting precise and accurate chemistry data is often challenging, chemistry data sets usually only span a small region of chemical space, which limits the performance and the scope of applicability of data-driven models. To address this issue, we integrated an active learning machine with automatic ab initio calculations to form a self-evolving model that can continuously adapt to new species appointed by the users. In the present work, we demonstrate the self-evolving concept by modeling the formation enthalpies of stable closed-shell polycyclic species calculated at the B3LYP/6-31G(2df,p) level of theory. By combining a molecular graph convolutional neural network with a dropout training strategy, the model we developed can predict density functional theory (DFT) enthalpies for a broad range of polycyclic species and assess the quality of each predicted value. For the species which the current model is uncertain about, the automatic ab initio calculations provide additional training data to i...
TL;DR: A new ReaxFF reactive force field has been developed for water-electrolyte systems including cations Li+, Na+, K+, and Cs+ and anions F-, Cl-, and I-.
Abstract: A new ReaxFF reactive force field has been developed for water-electrolyte systems including cations Li+, Na+, K+, and Cs+ and anions F-, Cl-, and I-. The reactive force field parameters have been trained against quantum mechanical (QM) calculations related to water binding energies, hydration energies and energies of proton transfer. The new force field has been validated by applying it to molecular dynamics (MD) simulations of the ionization of different electrolytes in water and comparison of the results with experimental observations and thermodynamics. Radial distribution functions (RDF) determined for most of the atom pairs (cation or anion with oxygen and hydrogen of water) show a good agreement with the RDF values obtained from DFT calculations. On the basis of the applied force field, the ReaxFF simulations have described the diffusion constants for water and electrolyte ions in alkali metal hydroxide and chloride salt solutions as a function of composition and electrolyte concentration. The obtained results open opportunities to advance ReaxFF methodology to a wide range of applications involving electrolyte ions and solutions.
TL;DR: V vibrational IR spectra of the protonated water clusters H7O3+ and H9O4+ (Eigen) in the range from 0 to 4000 cm-1 are reported from classical molecular dynamics and thermostated ring polymer molecular dynamics calculations, using recent high-level ab initio potential and dipole moments surfaces.
Abstract: We report vibrational IR spectra of the protonated water clusters H7O3+ and H9O4+ (Eigen) in the range from 0 to 4000 cm–1, from classical molecular dynamics (MD) and thermostated ring polymer mole...
TL;DR: The photophysical properties of dysprosium(III) triflate dissolved in H2O, MeOH, and DMSO have been studied in great detail and the emitted state is concluded to be 4F9/2, the m J levels must be considered when determining electronic energy levels, and scrutiny of the transition probabilities may reveal the structure of dys protonated and deuterated solvents in solution.
Abstract: Dysprosium(III) ions are the third most luminescent lanthanide(III) ions. Dy(III) is used as dopant in optical fibers and as shift reagent in NMR imaging and is the element at the forefront of research in single-molecule magnets. Nonetheless, the excited state manifold of the dysprosium(III) ion is not fully mapped and the nature of the emitting state has not been unequivocally assigned. In the work reported here, the photophysical properties of dysprosium(III) triflate dissolved in H2O, MeOH, and DMSO have been studied in great detail. The solvates are symmetric, all oxygen donor atom complexes where the coordination number is 8 or 9. By comparing protonated and deuterated solvents, performing variable temperature spectroscopy, and determining the excited state lifetimes and luminescence quantum yields, the solution structure can be inferred. For the three complexes, the observed electronic energy levels were determined using absorption and emission spectroscopy. The Dy(III) excited state manifolds of th...
TL;DR: Reaction of ammonia with SO3 as a potential source of sulfamic acid in the troposphere has been investigated by means of electronic structure and chemical kinetic calculations and results showed marked improvements.
Abstract: Reaction of ammonia with SO3 as a potential source of sulfamic acid in the troposphere has been investigated by means of electronic structure and chemical kinetic calculations. Besides, the hydrolysis reaction, which is known to be a major atmospheric decay channel of SO3, has also been investigated. The catalytic effects of ammonia and water on both the reactions have been studied. Rate coefficients for all the studied reaction channels were calculated using the transition state theory employing pre-equilibrium approximation. Calculated rate coefficients for a number of catalyzed hydrolysis and ammonolysis processes were found to be much higher (by ∼105 to ∼109 times) than the gas kinetic limit at ambient temperature. With decrease in temperature because of negative temperature dependence of rate coefficients, that difference became even larger (up to ∼1016 times). Therefore, in order to remove the discrepancies, rate coefficients for all the studied reaction channels were calculated by means of the mast...
TL;DR: The ability of alcohols to catalyze the 1,4-H transfer unimolecular decomposition of α-methyl substituted sCIs is demonstrated, suggesting that in regions with elevated alcohol concentrations, such as urban Brazil, these reactions may generate significant quantities of AAAHs and may begin to compete with sCI reactions with other trace tropospheric pollutants such as SO2.
Abstract: High-level ab initio calculations (DF-LCCSD(T)-F12a//B3LYP/aug-cc-pVTZ) are performed on a range of stabilized Criegee intermediate (sCI)–alcohol reactions, computing reaction coordinate energies, leading to the formation of α-alkoxyalkyl hydroperoxides (AAAHs). These potential energy surfaces are used to model bimolecular reaction kinetics over a range of temperatures. The calculations performed in this work reproduce the complicated temperature-dependent reaction rates of CH2OO and (CH3)2COO with methanol, which have previously been experimentally determined. This methodology is then extended to compute reaction rates of 22 different Criegee intermediates with methanol, including several intermediates derived from isoprene ozonolysis. In some cases, sCI–alcohol reaction rates approach those of sCI–(H2O)2. This suggests that in regions with elevated alcohol concentrations, such as urban Brazil, these reactions may generate significant quantities of AAAHs and may begin to compete with sCI reactions with o...
TL;DR: The (34,35) active space is large enough to give a qualitatively correct description of the orbital space and configuration space such that one obtains the correct spin state prediction when the external correlation energy is added accurately in a post-SCF step.
Abstract: Porphyrins are present in many metalloproteins, and they are also important components of a variety of nonbiological functional materials. Furthermore, they are representative of the kind of large, strongly correlated system that is especially difficult for accurate calculations. For example, predicting the order of their spin states has been challenging. Here we study the energetic order of four states (one singlet, two triplets, and one quintet) of iron porphyrin, FeP, by the multiconfiguration pair-density functional theory (MC-PDFT). Five active space prescriptions, namely, CAS(8, 6), CAS(8, 11), CAS(16, 15), RAS(34,2,2;13,6,16), and DMRG(34, 35), are used to obtain the kinetic energy, density, and on-top density. Although the prediction of which spin state of FeP is the ground state depends on the selection of the active space when one uses multireference second-order perturbation theory and such calculations lead incorrectly to a quintet ground state with the largest studied active space, all five active spaces correctly lead to a triplet ground state when one uses MC-PDFT. We conclude that the (34,35) active space is large enough to give a qualitatively correct description of the orbital space and configuration space such that one obtains the correct spin state prediction when the external correlation energy is added accurately in a post-SCF step. We also conclude that MC-PDFT can provide an efficient and accurate approach to treat the electron correlation in large, strongly correlated systems with the complexity of iron porphyrin.