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Spillover of adsorbed species from one active site to another is a key step in heterogeneous catalysis. However, the factors controlling this step, particularly the spillover of polyatomic species, have rarely been studied. Herein, we investigate the spillover dynamics of H* and CH3* species on a single‐atom alloy surface (Rh/Cu(111)) upon the dissociative chemisorption of methane (CH4), using molecular dynamics that considers both surface phonons and electron‐hole pairs. These dynamical calculations are made possible by a high‐dimensional potential energy surface machine learned from density functional theory data. Our results provide compelling evidence that the H* and CH3* can spill over on the metal surface at experimental temperatures and reveal novel dynamical features involving an internal motion during diffusion for CH3*. Increasing surface temperature has a minor effect on promoting spillover, as geminate recombinative desorption becomes more prevalent. However, the poisoning of the active site can be mitigated by the frequent gaseous molecular collisions that occur under ambient pressure in real‐world catalysis, which transfer energy to the trapped adsorbates. Interestingly, the bulky CH3* exhibits a significant spillover advantage over the light H* due to its larger size, which facilitates energy acquisition. These insights help to advance our understanding of spillover in heterogeneous catalysis. [ABSTRACT FROM AUTHOR]

Motivated by the captivating allure of exquisitely regulated characteristics exhibited by 2‐(2‐hydroxyphenyl)‐benzoxazole and its derivatives in the domains of photochemistry and photophysics, our current endeavor primarily focuses on delving into the intricacies of photo‐induced excited state reactions for derivatives of 2,5‐bis(benzoxazol‐2‐yl)‐thiophene‐3,4‐diol (BTD). Given the profound impact of chalcogen element doping, our primary focus lies in investigating the excited state behaviors of BTD‐O, BTD‐S, and BTD‐Se fluorophores. Through simulations encompassing variations in geometry and vertical excitation charge reorganization, we unveil atomic‐electronegativity‐dependent hydrogen bonding interactions and photoexcitation‐induced charge recombination that can significantly augment the intramolecular double proton transfer (ESDPT) reaction in the excited state for BTD‐O, BTD‐S, and BTD‐Se fluorophores. By constructing potential energy surfaces and identifying transition state forms, we elucidate the ultrafast stepwise ESDPT mechanism facilitated by the low potential barriers. Moreover, we rigorously validate the chalcogen atomic electronegativity‐driven regulation of the stepwise ESDPT mechanism. We sincerely anticipate that manipulating solvent polarity will pave the way for groundbreaking advancements in luminescent materials. [ABSTRACT FROM AUTHOR]

Vibrational spectroscopy enables critical insight into the structural and dynamic properties of molecules. Presently, the majority of theoretical approaches to spectroscopy employ wavefunction‐based ab initio or density functional methods that rely on the harmonic approximation. This approximation breaks down for large molecules with strongly anharmonic bonds or for molecules with large internuclear separations. An alternative to these methods involves generating molecular anharmonic potential energy surfaces (potentials) and using them to extrapolate the vibrational frequencies. This study examines the efficacy of density functional theory (DFT) and the correlation consistent Composite Approach (ccCA) in generating anharmonic frequencies from potentials of small main group molecules. Vibrational self‐consistent field Theory (VSCF) and post‐VSCF methods were used to calculate the fundamental frequencies of these molecules from their potentials. Functional choice, basis set selection, and mode‐coupling are also examined as factors in influencing accuracy. The absolute deviations for the calculated frequencies using potentials at the ccCA level of theory were lower than the potentials at the DFT level. With DFT resulting in bending modes that are better described than those of ccCA, a multilevel DFT:ccCA approach where DFT potentials are used for single vibrational mode potentials and ccCA is used for vibrational mode‐mode couplings can be utilized for larger polyatomic systems. The frequencies obtained with this multilevel approach using VCIPSI‐PT2 were closer to experimental frequencies than the scaled harmonic frequencies, indicating the success of utilizing post‐VSCF methods to generate more accurate representations of computed infrared spectra. [ABSTRACT FROM AUTHOR]

Recently, surface‐hopping ab initio molecular dynamics (SH‐AIMD) simulations have come to be used to discuss the mechanisms and dynamics of excited‐state chemical reactions, including internal conversion and intersystem crossing. In dynamics simulations involving intersystem crossing, there are two potential energy surfaces (PESs) governing the motion of nuclei: PES in a spin‐pure state and PES in a spin‐mixed state. The former gives wrong results for molecular systems with large spin‐orbit coupling (SOC), while the latter requires a potential gradient that includes a change in SOC at each point, making the computational cost very high. In this study, we systematically investigate the extent to which the magnitude of SOC affects the results of the spin‐pure state‐based dynamics simulations for the hydride MH2 (M = Si, Ge, Sn, Pb) by performing SH‐AIMD simulations based on spin‐pure and spin‐mixed states. It is clearly shown that spin‐mixed state PESs are indispensable for the dynamics simulation of intersystem crossing in systems containing elements Sn and Pb from the fifth period onward. Furthermore, in addition to the widely used Tully's fewest switches (TFS) algorithm, the Zhu‐Nakamura (ZN) global switching algorithm, which is computationally less expensive, is applied to SH for comparison. The results from TFS‐ and ZN‐SH‐AIMD methods are in qualitative agreement, suggesting that the less expensive ZN‐SH‐AIMD can be successfully utilized to investigate the dynamics of photochemical reactions based on quantum chemical calculations. [ABSTRACT FROM AUTHOR]

Transition state (TS) on the potential energy surface (PES) plays a key role in determining the kinetics and thermodynamics of chemical reactions. Inspired by the fact that the dynamics of complex systems are always driven by rare but significant transition events, we herein propose a TS search method in accordance with the Q‐learning algorithm. Appropriate reward functions are set for a given PES to optimize the reaction pathway through continuous trial and error, and then the TS can be obtained from the optimized reaction pathway. The validity of this Q‐learning method with reasonable settings of Q‐value table including actions, states, learning rate, greedy rate, discount rate, and so on, is exemplified in 2 two‐dimensional potential functions. In the applications of the Q‐learning method to two chemical reactions, it is demonstrated that the Q‐learning method can predict consistent TS and reaction pathway with those by ab initio calculations. Notably, the PES must be well prepared before using the Q‐learning method, and a coarse‐to‐fine PES scanning scheme is thus introduced to save the computational time while maintaining the accuracy of the Q‐learning prediction. This work offers a simple and reliable Q‐learning method to search for all possible TS and reaction pathway of a chemical reaction, which may be a new option for effectively exploring the PES in an extensive search manner. [ABSTRACT FROM AUTHOR]

Hydrogen spillover, involving the surface migration of dissociated hydrogen atoms from active metal sites to the relatively inert catalyst support, plays a crucial role in hydrogen‐involved catalytic processes. However, a comprehensive understanding of how H atoms are driven to spill over from active sites onto the catalyst support is still lacking. Here, we examine the atomic‐scale perspective of the H spillover process on a Pt/Cu(111) single atom alloy surface using machine‐learning accelerated molecular dynamics calculations based on density functional theory. Our results show that when an impinging H2 dissociates at an active Pt site, the Pt atom undergoes deactivation due to the dissociated hydrogen atoms that attach to it. Interestingly, collisions between H2 and sticking H atoms facilitate H spillover onto the host Cu, leading to the reactivation of the Pt atom and the realization of a continuous H spillover process. This work underscores the importance of the interaction between gas molecules and adsorbates as a driving force in elucidating chemical processes under a gaseous atmosphere, which has so far been underappreciated in thermodynamic studies. [ABSTRACT FROM AUTHOR]

Central‐atom effects on bimolecular nucleophilic substitution (SN2) reactions are well‐known in chemistry, however, the atomic‐level SN2 dynamics at phosphorous (P) centers has never been studied. We investigate the dynamics of the F−+PH2Cl reaction with the quasi‐classical trajectory method on a novel full‐dimensional analytical potential energy surface fitted on high‐level ab initio data. Our computations reveal intermediate dynamics compared to the F−+CH3Cl and the F−+NH2Cl SN2 reactions: phosphorus as central atom leads to a more indirect SN2 reaction with extensive complex‐formation with respect to the carbon‐centered one, however, the title reaction is more direct than its N‐centered pair. Stereospecificity, characteristic at C‐center, does not appear here either, due to the submerged front‐side‐attack retention path and the repeated entrance‐channel inversional motion, whereas the multi‐inversion mechanism discovered at nitrogen center is also undermined by the deep Walden‐well. At low collision energies, 6 % of the PH2F products form with retained configuration, mostly through complex‐mediated mechanisms, while this ratio reaches 24 % at the highest energy due to the increasing dominance of the direct front‐side mechanism and the smaller chance for hitting the deep Walden‐inversion minimum. Our results suggest pronounced central‐atom effects in SN2 reactions, which can fundamentally change their (stereo)dynamics. [ABSTRACT FROM AUTHOR]

Based on an analytical full‐dimensional potential energy surface (PES), named PES‐2022, fitted to high‐level ab initio calculations previously developed by our group and specifically developed to describe this polyatomic reactive process, an exhaustive kinetics analysis was performed in the temperature range 50–2000 K, that is, interstellar, atmospheric and combustion conditions. Using the competitive canonical unified theory with multidimensional tunneling corrections of small curvature, CCUS/SCT, and low‐ and high‐pressure limit (LPL and HPL) models, in this wide temperature range we found that the overall rate constants increase with temperature at T > 300 K and T < 200 K, showing a V‐shaped temperature dependence, reproducing the experimental evidence when the HPL model was used. The increase of the rate constant with temperature at low temperatures was due to the strong contribution of the tunneling factor. The title reaction evolves by two paths, H2O + CH2OH (R1) and H2O + CH3O (R2), and the branching ratio analysis showed that the R2 path was dominant at T < 200 K while the R1 path dominated at T > 300 K, with a turnover temperature of ∼260 K, in agreement with previous theoretical estimations. Three kinetics isotope effects (KIEs), 13CH3OH, CH318OH, and CD3OH, were theoretically studied, reproducing the experimental evidence. The kinetics analysis in the present paper together with the dynamics study previously reported showed the capacity of the PES‐2022 to understand this important chemical process. [ABSTRACT FROM AUTHOR]

The reaction HO + SO → H + SO2 (Rt) and its reverse (R‐t) play an important role in environment and the combustion of sulfur‐containing fuels. However, their kinetics is of high uncertainty as its reaction profile is complicated with multiple deep complexes and channels. In this work, the kinetics and mechanisms of Rt and R‐t are studied comprehensively based on a newly developed full‐dimensional accurate potential energy surface (PES) with the aid of machine learning. This highly accurate PES is interfaced with the software Gaussian. Then reliable information, including the energy, structures, and vibrational frequencies of the stationary points, as well as the minimum energy path and variational analysis can be efficiently determined. The variational transition state theory (VTST) and Rice−Ramsperger−Kassel−Marcus (RRKM) theory are employed to obtain the rate coefficients of each elementary reaction. The temperature‐ and pressure‐dependent rate coefficients of Rt are derived by the RRKM‐based master equation with hindered rotor and free rotor model considered. In addition, the effect of isotope substitution for the hydrogen is investigated on the reaction kinetics. Meanwhile, the quasi‐classical trajectory (QCT) calculation is performed on the PES‐2020 to obtain the temperature‐dependent reaction kinetics. [ABSTRACT FROM AUTHOR]

We demonstrate that a single polycyclic π‐scaffold can undergo sequential multistep excited‐state structural evolution along the bent, planar, and twisted conformers, which coexist to produce intrinsic multiple fluorescence emissions in room‐temperature solution. By installing a methyl or trifluoromethyl group on the ortho‐site of N,N′‐diphenyl‐dihydrodibenzo[a,c]phenazine (DPAC), the enhanced steric effects change the fluorescence emission of DPAC from a dominant red band to well‐resolved triple bands. The ultra‐broadband triple emissions of ortho‐substituted DPACs range from ≈350 to ≈850 nm, which is unprecedented for small fluorophores with molecular weight of <500. Ultrafast spectroscopy and theoretical calculations clearly reveal that the above dramatic changes originate from the influence of steric hindrance on the shape of excited state potential energy surface (S1 PES). Compared to the steep S1 PES of parental DPAC, the introduction of ortho‐substituent is shown to make the path of structural evolution in S1 wider and flatter, so the ortho‐substituted derivatives exhibit slower structural transformations from bent to planar and then to twisted forms, yielding intrinsic triple emission. The results provide the proof of concept that the bent, planar, and twisted emissive states can coexist in the same S1 PES, which greatly expand the fundamental understanding of the excited‐state structural relaxation. [ABSTRACT FROM AUTHOR]

Electronic structure calculations on small systems such as H2, H2O, LiH, and BeH2 with chemical accuracy are still a challenge for the current generation of noisy intermediate‐scale quantum (NISQ) devices. One of the reasons is that due to the device limitations, only minimal basis sets are commonly applied in quantum chemical calculations, which allows one to keep the number of qubits employed in the calculations at a minimum. However, the use of minimal basis sets leads to very large errors in the computed molecular energies as well as potential energy surface shapes. One way to increase the accuracy of electronic structure calculations is through the development of small basis sets better suited for quantum computing. In this work, we show that the use of adaptive basis sets, in which exponents and contraction coefficients depend on molecular structure, provides an easy way to dramatically improve the accuracy of quantum chemical calculations without the need to increase the basis set size and thus the number of qubits utilized in quantum circuits. As a proof of principle, we optimize an adaptive minimal basis set for quantum computing calculations on an H2 molecule, in which exponents and contraction coefficients depend on the HH distance, and apply it to the generation of H2 potential energy surface on IBM‐Q quantum devices. The adaptive minimal basis set reaches the accuracy of the double‐zeta basis sets, thus allowing one to perform double‐zeta quality calculations on quantum devices without the need to utilize twice as many qubits in simulations. This approach can be extended to other molecular systems and larger basis sets in a straightforward manner. [ABSTRACT FROM AUTHOR]

Inspired by the excellent photochemical properties of 2‐(2′‐hydroxyphenyl)benzazole and its derivatives, in this work, the novel 2‐bis(benzothia‐zolyl)naphthalene‐diol (2‐BBTND) fluorophore is explored about its photo‐induced behaviors. The intramolecular double hydrogen bonding interaction and the excited state intramolecular double proton transfer (ESDPT) behavior of 2‐BBTND fluorophore are investigated in combination with different polar solvent environments. From the structural changes and charge recombination induced by photoexcitation, we can affirm that strong polar solvent environment promotes the excited state dynamical reaction for 2‐BBTND compound. By constructing potential energy surfaces (PESs) in S0 and S1 states, we clarify that 2‐BBTND fluorophore should undergo the stepwise ESDPT reaction after photoexcitation. Combined with the size of potential energy barriers along with reaction paths in different solvents, we finally propose a new solvent‐polarity‐dependent stepwise ESDPT for 2‐BBTND fluorophore. [ABSTRACT FROM AUTHOR]

The open‐source statistical mechanics software described here, Arkane–Automated Reaction Kinetics and Network Exploration–facilitates computations of thermodynamic properties of chemical species, high‐pressure limit reaction rate coefficients, and pressure‐dependent rate coefficient over multi‐well molecular potential energy surfaces (PES) including the effects of collisional energy transfer on phenomenological kinetics. Arkane can use estimates to fill in information for molecules or reactions where quantum chemistry information is missing. The software solves the internal energy master equation for complex unimolecular reaction systems. Inputs to the software include converged electronic structure computations performed by the user using a variety of supported software packages (Gaussian, Molpro, Orca, TeraChem, Q‐Chem, Psi4). The software outputs high‐pressure limit rate coefficients and pressure‐dependent phenomenological rate coefficients, as well as computed thermodynamic properties (enthalpy, entropy, and constant pressure heat capacity) with added energy corrections. Some of the key features of Arkane include treatment of 1D, 2D or ND hindered internal rotation modes, treatment of free internal rotation modes, quantum tunneling effect consideration, transition state theory (TST) and Rice‐Ramsperger‐Kassel‐Marcus (RRKM) rate coefficient computations, master equation solution with four implemented methods, inverse‐Laplace transform of high‐pressure limit rate coefficients into the energy domain, energy corrections based on bond‐additivity or isodesmic reactions, automated and efficient PES exploration, and PES sensitivity analysis. The present work describes the design of Arkane, how it should be used, and refers to the theory that it employs. Arkane is distributed via the RMG‐Py software suite (https://github.com/ReactionMechanismGenerator/RMG‐Py). [ABSTRACT FROM AUTHOR]

Machine learning techniques have been widely applied in many fields of chemistry, physics, biology, and materials science. One of the most fruitful applications is machine learning of the complicated multidimensional function of potential energy or related electronic properties from discrete quantum chemical data. In particular, substantial efforts have been dedicated to developing various atomistic neural network (AtNN) representations, which refer to a family of methods expressing the targeted physical quantity as a sum of atomic components represented by atomic NNs. This class of approaches not only fully preserves the physical symmetry of the system but also scales linearly with respect to the size of a system, enabling accurate and efficient chemical dynamics and spectroscopic simulations in complicated systems and even a number of variably sized systems across the phases. In this review, we discuss different strategies in developing highly efficient and representable AtNN potentials, and in generalizing these scalar AtNN models to learn vectorial and tensorial quantities with the correct rotational equivariance. We also review active learning algorithms to generate practical AtNN models and present selected examples of AtNN applications in gas‐surface systems to demonstrate their capabilities of accurately representing both molecular systems and condensed phase systems. We conclude this review by pointing out remaining challenges for the further development of more reliable, transferable, and scalable AtNN representations in more application scenarios. This article is categorized under:Data Science > Artificial Intelligence/Machine LearningMolecular and Statistical Mechanics > Molecular Interactions [ABSTRACT FROM AUTHOR]

The results of a CCSD(T)‐F12/cc‐pVTZ‐f12//ωB97XD/cc‐pVTZ quantum‐chemical study of the potential energy surface (PES) for the reaction of propionitrile with methylidyne are combined with Rice‐Ramsperger‐Kassel‐Marcus (RRKM) calculations of the reaction rate constants and product branching ratios in the deep space conditions corresponding to the zero‐pressure limit at various collision energies. The most energetically favorable reaction pathways have been identified. The reaction outcome has been shown to strongly depend on the branching in the entrance reaction channel, between CH additions and insertions into various C‐H and C‐C bonds. For instance, CH addition to the N atom predominantly leads to 3H‐pyrrole + H (p9), with CH2NC + C2H4 (p2) also being a significant product. CH addition to the triple C≡N bond mostly results in 2‐methylene‐2H‐azirine + CH3 (p13), whereas CH insertions into C‐H bonds in the CH3 and CH2 groups of propionitrile form CH2CN + C2H4 (p1) and CH2CHCN + CH3 (p7) respectively. Less likely CH insertions into single C‐C bonds yield CH3CHCHCN + H (p5) and CH2CHCH2CN + H (p8). The results indicate that the methylidyne + propionitrile reaction may represent a critical step toward the formation of heterocyclic N‐containing molecules in the interstellar medium and in planetary atmospheres. [ABSTRACT FROM AUTHOR]

The nitrate radical is one of the most significant oxidants in troposphere at the nighttime. Furthermore, acrylic acid is reported to be one of 189 hazardous air pollutants. In order to investigate the atmospheric chemistry and environmental impact of acrylic acid with nitrate radical, in this work, the atmospheric reaction mechanisms of acrylic acid by NO3 radical have been discussed by the CCSD(T)/cc‐pVTZ//M06‐2X/6‐311++G(d, p) dual‐level of theory at the first time. The energy barriers of NO3 and CH2CHCOOH reaction have also been calculated accurately. The additions between NO3 with CH2CHCOOH would produce the dominant intermediates CH2NO3CHCOOH and CH2CHNO3COOH via low barriers. All hydrogen abstraction channels have higher barriers than that of additions. Therefore, addition pathways play an important role in this reaction. The total and branching rate constants have been computed by conventional transition state theory via the Variflex code. These rate constants of NO3 and acrylic acid reaction would be useful to complete structure–activity relationships of reaction rate. The calculated atmospheric lifetime of acrylic acid by NO3 is about 3.66 days at night. All findings will help us gain a better understanding of atmospheric chemistry of acrylic acid. [ABSTRACT FROM AUTHOR]

Machine learning (ML) models, neural networks, and Gaussian processes have been used to predict the potential energy surface taking C2‐He (both static and dynamic scenario) and NCCN‐He collision systems. The surface is restricted to ∽125 points where traditional spline becomes inefficacious. Quantum dynamics is performed by solving close‐coupling equation to compute cross sections benchmarking the performance of the ML models. The current study forms a basis for any future investigation of larger molecules where conventional fitting fails due to sparser ab initio points and cuts down the computational time without compromising on the quality of the surface. [ABSTRACT FROM AUTHOR]

Achieving wide‐range tunable emission colors, especially in the solid state of single‐fluorophore materials, remains a significant challenge. Herein, we report a molecular design strategy that affords wide‐range excitation‐dependent emissions spanning over ≈230 nm in crystalline states. Under the donor‐π‐acceptor configuration, we judiciously choose a rotatable acceptor fragment, o‐carborane, to enrich conformational diversities in the crystalline state and generate conformation‐dependent multicolor emissions. We further show that this molecular platform is generalizable in creating crystalline materials with multicolor emissions. Based on these materials, a high‐capacity information storage device and a finite‐state machine were fabricated to showcase multicolor displays and information storage. [ABSTRACT FROM AUTHOR]

The conformational manifold of psilocybin, a psychedelic molecule, was extensively explored using DFT method. Two most stable conformers were identified and the second most stable conformer was found to be 2.08 kcal/mol higher than the global minimum. The barrier of rotation between the two conformers was found to be 14.63 kcal/mol. The structural and spectroscopic parameters of both these conformers were similar. AIM (Atoms in molecule) calculation revealed very strong intramolecular H‐bond interactions in both the conformers. The structural parameters of these two conformers significantly matched with the earlier reported crystal structure of psilocybin. Further properties of these conformers were investigated using FMO (Frontier molecular orbital), AIM (Atoms in molecule), ESP (Electrostatic potential) calculations. UV (Ultraviolet)‐visible, IR (Infrared) and 1H‐NMR (Proton nuclear magnetic resonance) spectra were also computed. All the predicted results matched exceedingly well with the earlier reported literature. [ABSTRACT FROM AUTHOR]

The temperature dependence of the rate constants and the kinetics isotope effects of the OH + SiH4 hydrogen abstraction reaction were theoretically studied. Three different kinetics approaches were used in this study: variational transition state theory with multidimensional tunneling (VTST/MT) corrections, quasi‐classical trajectory (QCT) calculations, and ring polymer molecular dynamics (RPMD). These studies were performed on a global analytical potential energy surface based on explicitly correlated high level ab initio calculations developed in the present work. While the experimental rate constants are practically independent with temperature, the VTST/MT results show a pronounced dependence, the QCT partially corrects this behavior, and RPMD rates are in better agreement with experiment. In this case, in the experimental common temperature range, 300–600 K, the T‐expression for the RPMD rate constants is: k(T) = 6.40 × 10−13.T0.52exp(−0.10/T). The kinetics isotope effects, H/D, are small in this temperature range, revealing the small importance of tunneling effects in this very exothermic and low barrier reaction. Different factors, such as anharmonicity, the zero‐point violation problem or limitations of the surface, without ruling out experimental uncertainties, were analyzed to explain the discrepancies. [ABSTRACT FROM AUTHOR]

It is much more difficult to find on the potential energy surface (PES) a transition state (TS) than a local minimum (LM). We propose a new methodology which makes this task much easier. Applying external forces to nuclei in a molecule we can locate on PES not just one particular TS but a number of consecutive transition states. With our approach it is possible to move over PES from one transition state to another without involving any local minima. The latter can be located in a separate step through the reaction path calculations performed for every transition state found before. Preliminary results for the 2‐fluorofuran molecule illustrate the usefulness of the proposed method. [ABSTRACT FROM AUTHOR]

Density functional theory (DFT) and transition state theory(TST) were used to study the interaction between PuO2 and H2O. Firstly, we considered all possible spin states. The wave function was tested and optimized to get a stable configuration, and a minimal energy path(MEP) was derived so that the internuclear separations and interaction energy can be reasonably evaluated. Moreover, various topological analysis methods were used to investigate the changes in bonds during the interaction process. The localized orbital bonding analysis (LOBA) method was used to study the changes in the valence state of the product. The density of states diagram was drawn to analyze the contribution of 5 f orbital in the reaction process. And with the help of natural bond orbit (NBO) analysis, the bond orbit information was described. Finally, the reaction rate constant was calculated using the variational transition state theory (VTST). The current research provides necessary theoretical data support for the follow‐up related theoretical experimental research. [ABSTRACT FROM AUTHOR]

Potential energy surfaces for the H abstraction reactions by molecular oxygen from unsaturated closed‐shell C3–C5 hydrocarbons, including allene and propyne (C3H4), propene (C3H6), diacetylene (C4H2), vinylacetylene (C4H4), 1,3‐butadiene (C4H6), butene isomers (C4H8), cyclopentadiene (C5H6), and cyclopentene (C5H8), which were earlier identified among the main pyrolysis products of jet fuel components, have been explored at the CCSD(T)‐F12/cc‐pVTZ‐f12//ωB97XD/6‐311G** + ZPE(ωB97XD/6‐311G**) level of electronic structure theory. The results of the ab initio calculations were then utilized in transition state theory calculations of the reaction rate constants. The H abstraction reactions by O2 appeared to be most favorable from the allylic sites and from allene and propyne forming the propargyl radical, with the reactions involving the cyclic allylic sites in cyclopentadiene and cyclopentene exhibiting the lowest reaction endothermicities and barriers. They are followed by the reaction of O2 with cyclopentene producing cyclopent‐1‐en‐4‐yl and the reactions with vinylacetylene and 1,3‐butadiene forming the resonantly stabilized i‐C4H3 and i‐C4H5 radical products. The H abstractions from primary and secondary vinylic sites as well as from acetylenic sites are significantly less favorable and unlikely to compete. The calculated rate constants have been validated against the previous experimental and theoretical results for propene and butene isomers. All considered reactions of H abstraction by O2 are predicted to be rather slow, with their rate constants at 1500 K being on the order of 10–17‐10–16 cm3 molecule–1 s–1 and exhibiting a well‐defined Arrhenius behavior. Modified Arrhenius expressions for the reaction rate constants both in forward and reverse directions and Evans–Polanyi relationship between the activation and reaction energies have been generated and proposed for kinetic combustion models. The H abstractions by O2 forming the resonantly stabilized radicals were concluded to likely contribute to the initiation of oxidation of the unsaturated C3–C5 species produced in the pyrolysis of the important components of jet fuels. [ABSTRACT FROM AUTHOR]

The potential energy of molecular species and their conformers can be computed with a wide range of computational chemistry methods, from molecular mechanics to ab initio quantum chemistry. However, the proper choice of the computational approach based on computational cost and reliability of calculated energies is a dilemma, especially for large molecules. This dilemma is proved to be even more problematic for studies that require hundreds and thousands of calculations, such as drug discovery. On the other hand, driven by their pattern recognition capabilities, neural networks started to gain popularity in the computational chemistry community. During the last decade, many neural network potentials have been developed to predict a variety of chemical information of different systems. Neural network potentials are proved to predict chemical properties with accuracy comparable to quantum mechanical approaches but with the cost approaching molecular mechanics calculations. As a result, the development of more reliable, transferable, and extensible neural network potentials became an attractive field of study for researchers. In this review, we outlined an overview of the status of current neural network potentials and strategies to improve their accuracy. We provide recent examples of studies that prove the applicability of these potentials. We also discuss the capabilities and shortcomings of the current models and the challenges and future aspects of their development and applications. It is expected that this review would provide guidance for the development of neural network potentials and the exploitation of their applicability. This article is categorized under:Data Science > Artificial Intelligence/Machine LearningMolecular and Statistical Mechanics > Molecular InteractionsSoftware > Molecular Modeling [ABSTRACT FROM AUTHOR]

There has been tremendous advancement in machine learning (ML) applications in computational chemistry, particularly in neural network potentials (NNP). NNPs can approximate potential energy surface (PES) as a high dimensional function by learning from existing reference data, thereby circumventing the need to solve the electronic Schrödinger equation explicitly. As a result, ML accelerates chemical space exploration and property prediction compared to quantum mechanical methods. Novel ML methods have the potential to provide efficient means for predicting the properties of molecules. However, this potential has been limited by the lack of standard comparative evaluations. In this work, we compare four selected models, that is, ANI, PhysNet, SchNet, and BAND‐NN, developed to represent the PES of small organic molecules. We evaluate these models for their accuracy and transferability on two different test sets (i) Small organic molecules of up to eight‐heavy atoms on which ANI and SchNet achieve root mean square error (RMSE) of 0.55 and 0.60 kcal/mol, respectively. (ii) On random selection of molecules from the GDB‐11 database with 10‐heavy atoms, ANI achieves RMSE of 1.17 kcal/mol and SchNet achieves RMSE of 1.89 kcal/mol. We examine their ability to produce smooth meaningful surface by performing PES scans for bond stretch, angle bend, and dihedral rotations on relatively large molecules to assess their possible application in molecular dynamics simulations. We also evaluate their performance for yielding minimum energy structures via geometry optimization using various minimization algorithms. All these models were also able to accurately differentiate different isomers of the same empirical formula C10H20. ANI and PhysNet achieve an RMSE of 0.29 and 0.52 kcal/mol, respectively, on C10H20 isomers. [ABSTRACT FROM AUTHOR]

Theoretical understanding of thiophene clusters is very important for molecular understanding of thiophene as solvent and for determining the thermodynamics properties of the solvent. However, no investigations on thiophene clusters have been reported previously in the literature. We have performed in this work an ab initio computational study to understand the interactions taking place in thiophene clusters using the thiophene pentamer. We started by generating possible structures using classical molecular dynamics followed by full optimization at the ab initio MP2/aug‐cc‐pVDZ level of theory. Relative energies and temperature‐dependent isomer distribution of the investigated structures have been reported. Finally, we have performed a quantum theory of atoms in molecule (QTAIM) analysis to identify all non‐covalent bondings that are responsible for the stability of the structures of the thiophene pentamer. The results show that six different types of non‐covalent interactions could be found in thiophene pentamer depending on the structure. [ABSTRACT FROM AUTHOR]

The potential energy surfaces (PESs) and band gap landscapes (BGLs) of MoS2 and TiS2 monolayers were studied with a set of density functional methods. For our best knowledge, the PESs for transition metal dichalcogenides as a function of sulfur atom coordinates were studied for the first time. It is found that the energy differences between chemically meaningful points of the PESs are quite stable with respect to the density functional choice. The BGLs are characterized by "wavelike" structure with maxima that refer to 2H forms and minima that refer to 1T forms and ripples between them. It is shown that thermal vibrations may reduce the band gap in 2H form of MoS2. [ABSTRACT FROM AUTHOR]

In the past a few years, there has been significant progress in theoretical characterizations of gas‐surface reaction dynamics at the atomic level. One of the major breakthroughs is the machine learning representations of the potential energy surfaces and related properties for molecules on metal surfaces from first‐principles, particularly neural networks based methods. In this review, we focus on recent advances of the development and applications of high‐dimensional symmetry‐preserving neural network representations in gas‐surface systems, which have enabled efficient Born‐Oppenheimer molecular dynamics simulations with inclusion of all molecular and surface degrees of freedom, as well as some nonadiabatic molecular dynamics simulations with effective treatment of hot electrons, at the density function theory level. Despite these advances, further challenges remain. More accurate electronic structure theories and more efficient machine learning (and active learning) algorithms are needed towards a more quantitative description of more complex gas‐surface reactions involving multiple surfaces and adsorbates or multiple electronic states. [ABSTRACT FROM AUTHOR]

The rate coefficients of ethynyl radical reaction with n‐butane were computed for the first time using the canonical variational transition state theory (CVT) between 150 and 5000 K. The structures and frequencies of all the stationary points are computed at the M06‐2X/6‐31+G(d,p) level of theory. The potential energy surface scanned shows that two rotamers exist for n‐butane. Three different transition states were identified for each rotamers. The rate coefficients obtained over the temperature range of 150–500 K using the M06‐2X/6‐31+G(d,p) theory were used to derive the Arrhenius expression: k(T) = 1.35 × 10−17 T2.0 exp[1326/T] cm3 molecule−1 s−1. It is shown that the H‐abstraction from –CH2– group of n‐butane is the dominant reaction channel over the complete temperature range. [ABSTRACT FROM AUTHOR]

The potential energy surfaces of the Vinylogous Wolff Rearrangement, an alternative process for the Wolff Rearrangement that takes place β,γ‐unsaturated diazoketones have been fully explored employing M062X model chemistry and in a complementary task by means of the CASSCF method. The NBO analysis has been invoked to reveal the alternations of orbital occupancies and their stabilization energies through some of the critical structures located on the pathways. The calculations establish a two steps process for each pathway involving a second higher energy transition state that seems likely to be the rate determining step in agreement with experimental results. Energy analysis indicates more feasibility of the pathway including diradical intermediate. The most striking feature of the study concerns the finding out a transition state providing a channel in between two pathways through interconversion of the two keys bicyclo[2.1.0]pentanone and diradical intermediates. [ABSTRACT FROM AUTHOR]

In the past a few years, there has been significant progress in theoretical characterizations of gas‐surface reaction dynamics at the atomic level. One of the major breakthroughs is the machine learning representations of the potential energy surfaces and related properties for molecules on metal surfaces from first‐principles, particularly neural networks based methods. In this review, we focus on recent advances of the development and applications of high‐dimensional symmetry‐preserving neural network representations in gas‐surface systems, which have enabled efficient Born‐Oppenheimer molecular dynamics simulations with inclusion of all molecular and surface degrees of freedom, as well as some nonadiabatic molecular dynamics simulations with effective treatment of hot electrons, at the density function theory level. Despite these advances, further challenges remain. More accurate electronic structure theories and more efficient machine learning (and active learning) algorithms are needed towards a more quantitative description of more complex gas‐surface reactions involving multiple surfaces and adsorbates or multiple electronic states. [ABSTRACT FROM AUTHOR]

Chemical clusters are relevant to many applications in catalysis, separations, materials, and energy sciences. Experimentally, the structure of clusters is difficult to determine, but it is very important in understanding their chemistry and properties. Computational methods can be used to examine cluster structure, however finding the most stable structure is not simple, particularly as the cluster size increases. Global optimization techniques have long been used to tackle the problem of the most stable structure, but such approaches would have to look for a global minimum, while sampling local minima over the whole potential energy surface as well. In this review, the state‐of‐the‐art theory of global optimization theory is summarized. First, the definition, significance, relation to experiments, and a brief history of global optimization is presented. We then discuss, in more detail, three versatile global optimization methods: the basin hopping, the artificial bee colony algorithm, and the genetic algorithm. We close with some representative application examples of global optimization of clusters since 2016 and the challenges, open questions and opportunities in this field. [ABSTRACT FROM AUTHOR]

The reaction of CH3 + HCNO was theoretically studied by both density functional theory and molecular orbital calculations and analyzed by quantum statistical methods. The potential energy surface was constructed at the UCCSD(T)//B3LYP/6‐311++G(3df,2p) + ZPE level. Four entrance channels are opened relating to the interaction of the CH3 radical with each of the four atoms of the HCNO molecule, giving rise to 18 different product sets. The predicted geometries and heats of reaction are in good agreement with available experimental data. The major pathways involve addition of CH3 to the C atom of HCNO with a small energy barrier of ∼4 kcal/mol forming both Z and E‐HC(CH3)NO (IS1/IS1b) intermediates lying 45 or 44 kcal/mol, respectively, below the reactants. The nascent intermediates can collisionally be deactivated and subsequently decomposed into H + CH3CNO or isomerized prior to decomposition giving other products. Kinetics calculations covering the temperature range of 400‐2500 K, under pressures of 7.6 × 10–1 to 7.6 × 105 Torr for N2, He, and Ar as the third bodies show that at 760 Torr N2, the adducts including both IS1 and IS1b are the major products at temperature below 600 K, whereas H + CH3CNO and CNO + CH4 are the major products at T ≥ 1500 K. The total high‐pressure rate coefficient can well be expressed by the following three‐parameter equation: k(T) = 7.75 × 10–16 T1.69 exp (−1480 K/T) cm3 molecule–1 s–1. [ABSTRACT FROM AUTHOR]

We report the ground state tunneling splittings (ΔE±) of a number of axially chiral molecules using the ring‐polymer instanton (RPI) method (J. Chem. Phys., 2011, 134, 054109). The list includes isotopomers of hydrogen dichalcogenides H2X2 (X = O, S, Se, Te, and Po), hydrogen thioperoxide HSOH and dichlorodisulfane S2Cl2. Ab initio electronic‐structure calculations have been performed on the level of second‐order Møller–Plesset perturbation (MP2) theory either with split‐valance basis sets or augmented correlation‐consistent basis sets on H, O, S, and Cl atoms. Energy‐consistent pseudopotential and corresponding triple zeta basis sets of the Stuttgart group are used on Se, Te, and Po atoms. The results are further improved using single point calculations performed at the coupled cluster level with iterative singles and doubles and perturbative triples amplitudes. When available for comparison, our computed values of ΔE± are found to lie within the same order of magnitude as values reported in the literature, although RPI also provides predictions for H2Po2 and S2Cl2, which have not previously been directly calculated. Since RPI is a single‐shot method which does not require detailed prior knowledge of the optimal tunneling path, it offers an effective way for estimating the tunneling dynamics of more complex chiral molecules, and especially those with small tunneling splittings. [ABSTRACT FROM AUTHOR]

The mechanism of initial decomposition of energetic compound is crucial to understand the heat release efficiency, impact sensitivity, toxic emission, and so on. In the present study, we progressively explored the thermodynamic and kinetic features of the decomposition of LLM‐105, or 2,6‐diamino‐3,5‐dinitropyrazine‐1‐oxide, a kind of nitro compound in energetic materials using theoretical calculations. The bond dissociation energies (BDEs), bond orders, and the decomposition pathways were investigated by high‐level quantum chemical calculations, and the temperature‐ and pressure‐dependent rate coefficients were computed by Rice‐Ramsperger‐Kassel‐Marcus (RRKM)/master equation simulations. Although thermodynamic properties, for example, BDEs and bond orders, provide preliminary estimates on a possible decomposition mechanism including trigger bonds with relatively low computational costs, kinetic studies are necessary to determine all reaction pathways and competition relationships among various pathways. The potential energy surface at the theoretical level of DLPNO‐CCSD(T)/CBS//M06‐2X‐D3/6‐311++G(d,p) reveals the complicated decomposition mechanism including the bottlenecks of all channels. The computed rate coefficients showthat the reaction channels yielding NO2 will dominate the initial decomposition at high temperature (>1000 K), while the NO elimination channels play a controlling role at low temperature (<800 K). [ABSTRACT FROM AUTHOR]

A mathematical aspect of the anharmonic downward distortion following (ADDF) path is discussed. The ADDF method is utilized as an automated reaction path search method, which can explore transition state geometries on a potential energy surface from a potential minimum. We show that the maximum number of the ADD stationary paths intersecting the potential minimum is 2f + 1 − 2, where f denotes the degree of freedom of the system. We also show that the bifurcation of the ADD stationary path is essential to detect all the transition states connected from a given minimum. The ADDF computation is demonstrated for a H2O molecule in which pitchfork bifurcation is observed. [ABSTRACT FROM AUTHOR]

The OH‐based excited‐state intramolecular proton transfer (ESIPT) of 2‐(5‐(4‐carboxyphenyl)‐2‐hydroxyphenyl)benzothiazole (CHBT) derivatives (4R‐CHBT) that were replaced by electron‐donating groups (CH3, OH) and electron‐withdrawing groups (COOH, CF3, CN) have been studied by the time‐dependent density functional theory (TD‐DFT) method. We analyzed structural parameters, infrared (IR) vibrational spectrum, frontier molecular orbitals (FMOs), and electronic spectra, which can describe the trend of ESIPT process. The constructed potential energy surfaces showed that the ESIPT potential energy barriers of 4R‐CHBT are in the range of 0.25 to 0.62 kcal/mol, which are just a little bigger than that value of CHBT. All the chosen substituents, no matter electron‐donating or electron‐withdrawing groups, make ESIPT processes slightly more difficult. [ABSTRACT FROM AUTHOR]

Model chemistry G3(MP2,CC)//B3LYP/6‐311G(d,p) calculations of the potential energy surface for the reaction of phenyl radical (C6H5) with phenylacetylene (C8H6) have been carried out and combined with Rice‐Ramsperger‐Kassel‐Marcus/Master Equation calculations of temperature‐ and pressure‐dependent rate constants. The results showed that the reaction can serve as a viable source for the formation of phenanthrene via an indirect route involving a primary reaction of phenyl addition to the ortho carbon in the ring of phenylacetylene and H elimination producing 2‐ethynylbiphenyl followed by secondary H‐assisted isomerization of 2‐ethynylbiphenyl to phenanthrene. In the secondary reaction, the H atom adds to the α carbon of the ethynyl side chain, then a six‐member ring closure takes place followed by aromatization via an H loss. The channel of H addition to the side chain of 2‐ethynylbiphenyl appears to be much faster than H addition to the ortho carbon in the ethynyl‐substituted ring leading back to the initial C6H5 + C8H6 reactants. Rate constants for the primary C6H5 + C8H6←→2‐ethynylbiphenyl (p1) + H and secondary p1 + H←→phenanthrene (p2) + H reactions have been computed in the temperature range of 500‐2500 K at pressures of 30 Torr, 1, 10, and 100 atm and fitted to modified Arrhenius expressions. The suggested kinetic scheme and rate constants are proposed as a prototype for the modeling of the growth of polycyclic aromatic hydrocarbons via the phenyl addition‐dehydrocyclization (PAC) mechanism involving an addition of a PAH radical to an ethynyl‐substituted PAH molecule. [ABSTRACT FROM AUTHOR]

3‐Carene is an important potential biofuel with properties similar to the jet‐propellant JP‐10. Its thermal decomposition and combustion behavior is to date unknown, which is essential to assess its quality as a fuel. A combined experimental and kinetic modeling study has been conducted to understand the initial decomposition of 3‐carene. The pyrolysis of 3‐carene was investigated in a jet‐stirred quartz reactor at atmospheric pressure, at temperatures varying from 650 to 1050 K, covering the complete conversion range. The decomposition of 3‐carene was observed to start around 800 K, and it is almost complete at 970 K. Online gas chromatography shows that primarily aromatics are generated which suggests that 3‐carene is not a good fuel candidate. The potential energy surface for the initial decomposition pathways determined by KinBot shows that a hydrogen elimination reaction dominates, giving primarily cara‐2,4‐diene. Next to this molecular pathway, radical pathways lead to aromatics via ring opening. The kinetic model was automatically generated with Genesys and consists of 2565 species and 9331 reactions. New quantum chemical calculations at the CBS‐QB3 level of theory were needed to calculate rate coefficients and thermodynamic properties relevant for the primary decomposition of 3‐carene. Both the conversion of 3‐carene and the yields of the primary products (ie, benzene and hydrogen gas) are well predicted with this kinetic model. Rate of production analyses shows that the dominant pathways to convert 3‐carene are hydrogen elimination reaction and radical chemistry. [ABSTRACT FROM AUTHOR]

The current work demonstrates the application of topography‐based Gaussian charge models (GCMs) in studying potential energy surfaces of molecular dimers of water, ammonia, acetylene and benzene in addition to water‐ammonia, water‐acetylene, ammonia‐acetylene, water‐benzene, ammonia‐benzene and acetylene‐benzene complexes. Investigations are also carried for trimer systems of water, ammonia and their mixed compositions. The predicted geometries are in good agreement with those derived from quantum mechanical (QM) calculations and the interaction energy values forecasted deviate not more than ±2 kcal/mol from respective QM counterparts. [ABSTRACT FROM AUTHOR]

The adiabatic mechanism of the reaction of trichloroethylene with O(3P), exploring the various O‐atom addition and H‐atom abstraction channels, is theoretically studied at the MP2/6‐311++G(2d, 2p), MP2/aug‐cc‐pVTZ, CCSD/6‐31G(d), G3, and CBS‐QB3 levels of theory. From a kinetic point of view, the addition to the less substituted carbon atom of the double bond is more favorable than the addition to the more substituted carbon. Such O‐atom addition reactions are favored over the one possible hydrogen‐abstraction reaction. Calculations of the present study showed that five products are obtained: HCCl + C(O)Cl2 (P1), Cl + ClC(O)CHCl (P2), H + ClC(O)CCl2 (P3), Cl + HC(O)CCl2 (P4), and CH(O)Cl + CCl2 (P5). The products P2 and P4 are found to be the most favored ones. The kinetic calculations of rate constant in the range of 285–395 K are performed at the CBS‐QB3 level of theory and are in conformity with the experimental outcomes. [ABSTRACT FROM AUTHOR]

We report an exhaustive conformational and electronic study on dopamine (DA) interacting with the D2 dopamine receptor (D2DR). For the first time, the complete surface of the conformational potential energy of the complex DA/D2DR is reported. Such a surface was obtained through the use of QM/MM calculations. A detailed study of the molecular interactions that stabilize and destabilize the different molecular complexes was carried out using two techniques: Quantum Theory of Atoms in Molecules computations and nuclear magnetic shielding constants calculations. A comparative study of the behavior of DA in the gas phase, aqueous solution, and in the active site of D2DR has allowed us to evaluate the degree of deformation suffered by the ligand and, therefore, analyze how rustic are the lock‐key model and the induced fit theory in this case. Our results allow us to propose one of the conformations obtained as the "biologically relevant" conformation of DA when it is interacting with the D2DR. [ABSTRACT FROM AUTHOR]

The virtual‐reality framework AVATAR (Advanced Virtual Approach to Topological Analysis of Reactivity) for the immersive exploration of potential‐energy landscapes is presented. AVATAR is based on modern consumer‐grade virtual‐reality technology and builds on two key concepts: (a) the reduction of the dimensionality of the potential‐energy surface to two process‐tailored, physically meaningful generalized coordinates, and (b) the analogy between the evolution of a chemical process and a pathway through valleys (potential wells) and mountain passes (saddle points) of the associated potential energy landscape. Examples including the discovery of competitive reaction paths in simple A + BC collisional systems and the interconversion between conformers in ring‐puckering motions of flexible rings highlight the innovation potential that augmented and virtual reality convey for teaching, training, and supporting research in chemistry. [ABSTRACT FROM AUTHOR]

Quantum chemical explorations of potential energy surfaces showed that acetylene produces various products starting from molecular arrays in short distances of 1.3–2.5 Å. Arrays of (C2H2)2 gave cyclobutadiene, tetrahedrane, and acetylene dimers. Arrays of (C2H2)3 gave benzene, prismane, benzvalene, Dewar benzene, and acetylene trimers. Arrays of (C2H2)4 gave cubane, cyclooctatetranene, and acetylene tetramers. Different forms of initial arrays yielded different sets of products; a parallel array of two monomers gave cyclobutadiene, whereas a cross array gave tetrahedrane. Initial molecular arrays with unusually close contacts were estimated to require local forces of 1–9 × 10−8 N. © 2019 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Molecular dynamics (MD) provide predictive understanding of the behavior of condensed matter. However, its true potential remains largely untested because relevant timescales are often inaccessible, limited portions of conformation space get sampled, and infrequent events are usually irreproducible. A culprit is the huge informational burden required to iterate integration steps. To address the problem, deep learning is applied to encode the dynamics into a shorthand embodiment retaining only essential topological features of the vector field that steers MD integration. The flow is simplified via an equivalence relation that identifies conformations within basins of attraction in potential energy and encodes the dynamics onto a modulo‐basin "quotient space" where fast motions are averaged out. The quotient space projection enables coverage of realistic timescales while unraveling the underlying dynamic hierarchy. Deep learning is exploited to propagate the simplified trajectory beyond MD‐accessible timescales and to reconstruct it at atomistic level. As shown, the quotient‐encoding‐propagating‐decoding scheme generates within a few hours protein folding pathways with experimentally verified outcomes. By contrast, MD computations covering comparable timespans would take over a hundred days on special‐purpose supercomputers. Thus, quotient space constitutes a model for hierarchical understanding of MD simulation while enabling access to realistic timescales. [ABSTRACT FROM AUTHOR]

Accurate structure and potential energy surface of germylene, GeH2, in its ground electronic state X˜1A1 were determined from ab initio calculations using the coupled‐cluster approach in conjunction with the correlation‐consistent basis sets up to sextuple‐zeta quality. The Born‐Oppenheimer equilibrium structural parameters for the X˜1A1 state are estimated to be re(GeH) = 1.5793 Å and ∠e(HGeH) = 91.19∘. The term value Te for the lowest excited electronic state ã3B1 of GeH2 is predicted to be 9140 cm–1. The vibration‐rotation energy levels for the X˜1A1 state of the 74GeH2, 74GeD2, 72GeH2, and 70GeH2 isotopologues were determined using a variational approach and compared with the experimental data. The role of the core‐electron correlation, higher‐order valence‐electron correlation, scalar relativistic, spin‐orbit, and adiabatic effects for prediction of the structure and vibration‐rotation dynamics of the GeH2 molecule is discussed. © 2019 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Accurate structure and potential energy surface of germylene, GeH2, in its ground electronic state X˜1A1 were determined from ab initio calculations using the coupled‐cluster approach in conjunction with the correlation‐consistent basis sets up to sextuple‐zeta quality. The Born‐Oppenheimer equilibrium structural parameters for the X˜1A1 state are estimated to be re(GeH) = 1.5793 Å and ∠e(HGeH) = 91.19∘. The term value Te for the lowest excited electronic state ã3B1 of GeH2 is predicted to be 9140 cm–1. The vibration‐rotation energy levels for the X˜1A1 state of the 74GeH2, 74GeD2, 72GeH2, and 70GeH2 isotopologues were determined using a variational approach and compared with the experimental data. The role of the core‐electron correlation, higher‐order valence‐electron correlation, scalar relativistic, spin‐orbit, and adiabatic effects for prediction of the structure and vibration‐rotation dynamics of the GeH2 molecule is discussed. © 2019 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

An accurate potential energy surface for the ground electronic state of SH3 system has been constructed with 41,882 high level ab initio energy points and the neural network fitting method. The time‐dependent wave packet method has been used to calculate the first state‐to‐state differential cross sections for the title reaction up to 1.2 eV in full dimensions, based on the reactant–product decoupling scheme. It is found that the majority of H2S are produced in the ground vibrational state, with a large fraction of available energy for the reaction ending up as product translational motion. The differential cross sections at the threshold energy are dominated by a very narrow peak in the backward direction. With the increase of collision energy, the width of the angular distribution increases considerably, which is a typical feature of a direct reaction via abstract mechanism, similar to the H2 + OH → H2O + H reaction. © 2018 Wiley Periodicals, Inc. The authors construct a potential energy surface for the ground electronic state of the SH3 system with high level ab initio energy points and the neural network fitting method. Based on this new potential energy surfaces, they report the first full‐dimensional (6D) state‐to‐state differential cross sections up to 1.2 eV from the ground rovibrational initial state, using the reactant–product decoupling scheme‐based time‐dependent wave packet method. [ABSTRACT FROM AUTHOR]

Ab initio and density functional CCSD(T)‐F12/cc‐pVQZ‐f12//B2PLYPD3/6‐311G** calculations have been performed to unravel the reaction mechanism of triplet and singlet methylene CH2 with ketene CH2CO. The computed potential energy diagrams and molecular properties have been then utilized in Rice–Ramsperger–Kassel–Marcus‐Master Equation (RRKM‐ME) calculations of the reaction rate constants and product branching ratios combined with the use of nonadiabatic transition state theory for spin‐forbidden triplet‐singlet isomerization. The results indicate that the most important channels of the reaction of ketene with triplet methylene lead to the formation of the HCCO + CH3 and C2H4 + CO products, where the former channel is preferable at higher temperatures from 1000 K and above. In the C2H4 + CO product pair, the ethylene molecule can be formed either adiabatically in the triplet electronic state or via triplet‐singlet intersystem crossing in the singlet electronic state occurring in the vicinity of the CH2COCH2 intermediate or along the pathway of CO elimination from the initial CH2CH2CO complex. The predominant products of the reaction of ketene with singlet methylene have been shown to be C2H4 + CO. The formation of these products mostly proceeds via a well‐skipping mechanism but at high pressures may to some extent involve collisional stabilization of the CH3CHCO and cyclic CH2COCH2 intermediates followed by their thermal unimolecular decomposition. The calculated rate constants at different pressures from 0.01 to 100 atm have been fitted by the modified Arrhenius expressions in the temperature range of 300–3000 K, which are proposed for kinetic modeling of ketene reactions in combustion. © 2018 Wiley Periodicals, Inc. The reaction mechanism of triplet and singlet methylene CH2 with ketene CH2CO is revealed through calculations of potential energy surfaces and rate constants for different product channels. The triplet reaction mostly forms the HCCO + CH3 and C2H4 + CO products, where the former channel is preferable at higher temperatures above 1000 K. Ethylene can be produced both in triplet and singlet states via intersystem crossing. The singlet reaction produces singlet ethylene + CO. [ABSTRACT FROM AUTHOR]

Alternatively, DAP can undergo the deamination twice by adding two H SB 2 sb O consecutively to form iCyt (reaction 5) and Ura (reaction 6). This prediction explains reasonably the aforementioned respective yields of 0.05%, 0.75%, 10.8% for the production of Cyt, iCyt, and Ura from the reaction of CAA and GD in aqueous solution. The high overall activation energies of a few hundreds kJ/mol obtained for the suggested reactions eliminate the possibility of thermal reactions to form Cyt or Ura in the gas phase of the interstellar medium (ISM). Although the result predicts that the formation of Cyt or Ura does not occur by thermal reactions in the gas phase of the ISM due to high reaction barriers, its occurrence in the icy-grain of the ISM cannot be entirely eliminated. [Extracted from the article]