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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]

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]

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]

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]

Abstract: A new global potential energy surface for the ground state of MgH2 was constructed using the permutation invariant polynomial neural network method. About 70 000 ab initio energy points were calculated via the multi‐reference configuration interaction method method with aug‐cc‐pVTZ and aug‐cc‐pVQZ basis sets, and these points were used to construct the potential energy surface (PES). To avoid basis set superposition error, the basis set was extrapolated to the complete basis set limit using the two point energy extrapolation formula. The root mean square error of the present PES is only 8.85 meV. Initial state (v = 0, j = 0) dynamics studies were performed using the time‐dependent wave packet method with a second‐order split operator for the total angular momentum J up to a value of 50. Furthermore, the reaction probability, integral cross section, and thermal rate constant are reported and compared with available theoretical studies. [ABSTRACT FROM AUTHOR]

Abstract: A new global potential energy surface for the ground state of MgH2 was constructed using the permutation invariant polynomial neural network method. About 70 000 ab initio energy points were calculated via the multi‐reference configuration interaction method method with aug‐cc‐pVTZ and aug‐cc‐pVQZ basis sets, and these points were used to construct the potential energy surface (PES). To avoid basis set superposition error, the basis set was extrapolated to the complete basis set limit using the two point energy extrapolation formula. The root mean square error of the present PES is only 8.85 meV. Initial state (v = 0, j = 0) dynamics studies were performed using the time‐dependent wave packet method with a second‐order split operator for the total angular momentum J up to a value of 50. Furthermore, the reaction probability, integral cross section, and thermal rate constant are reported and compared with available theoretical studies. [ABSTRACT FROM AUTHOR]

Abstract: In this work, we present a quantum mechanical treatment of the three‐body LiH 2 + molecular system in the Born–Oppenheimer (BO) approximation, were the nuclei dynamics is evaluated over the potential energy surfaces (PES) induced by the electronic states. The PES corresponding to the two lowest electronic levels are the ones described by Martinazzo et al. (Chem. Phys. 2003, 287, 335), and are used to write the three‐body Schrdinger equation of the three atomic system. We use the generalized Sturmian functions method to expand the wave functions in each (distinguishable) pair of relative coordinates or Jacobi pairs, and analyze the convergence differences between the series. A partial‐wave decomposition of the potential is proposed to simplify the Hamiltonian matrix element calculation. Bound states are considered for the ground and first excited electronic PES, the spreading of energies after sudden electronic transitions studied, and the break‐up probability induced by the sudden change of the PES evidenced. [ABSTRACT FROM AUTHOR]

A global potential energy surface (PES) corresponding to the ground state of AuH2 system has been constructed based on 22 853 ab initio energies calculated by the multireference configuration interaction method with a Davidson correction. The neural network method is used to fit the PES, and the root mean square error is only 1.87 meV. The topographical features of the novel global PES are compared with previous PES which is constructed by Zanchet et al. (Zanchet PES). The global minimum energy reaction paths on the two PESs both have a well and a barrier. Relative to the Au + H2 reactants, the energy of well is 0.316 eV on the new PES, which is 0.421 eV deeper than Zanchet PES. The calculation of Au(2S) + H2(X1Σg+) → AuH(X1Σ+) + H(2S) dynamical reaction is carried out on new PES, by the time-dependent quantum wave packet method (TDWP) with second order split operator. The reaction probabilities, integral cross-sections (ICSs) and differential cross-sections are obtained from the dynamics calculation. The threshold in the reaction is about 1.46 eV, which is 0.07 eV smaller than Zanchet PES due to the different endothermic energies on the two PESs. At low collision energy (<2.3 eV), the total ICS is larger than the result obtained on Zanchet PES, which can be attributed to the difference of the wells and endothermic energies. [ABSTRACT FROM AUTHOR]

A global potential energy surface (PES) for the electronic ground state of Li2H system is constructed over a large configuration space. About 30 000 ab initio energy points have been calculated by MRCI-F12 method with aug-cc-pVTZ basis set. The neural network method is applied to fit the PES and the root mean square error of the current PES is only 1.296 meV. The reaction dynamics of the title reaction has been carried out by employing time-dependent wave packet approach with second order split operator on the new PES. The reaction probability, integral cross section and thermal rate constant are obtained from the dynamics calculation. In most of the collision energy regions, the integral cross sections are in well agreement with the results reported by Gao et al. The rate constant calculated from the new PES increases in the temperature range of present investigation. [ABSTRACT FROM AUTHOR]

The geometric and electronic structures of a series of silicon fluorides [ABSTRACT FROM AUTHOR]

The noncovalent halogen···halogen (X···X) interaction, which shows significant anisotropic feature, is extensively used in rationally designing supramolecular assemblies. Here, beyond the binding energy of stable geometries, the anisotropic topology of the potential energy surface (PES) is explored. We show that most functionals of DFT give remarkably unphysical angular distortion of the PES. This is unlikely to be solved unless the components that ensure correct angular dependent behavior in the halogen bonding region are contained in the functionals. We also prove that simple empirical corrections may substantially quantify this unphysical angular distortion, and further investigation is recommended. These findings constitute a step forward toward the understanding of the nature of X···X bonds, and provide some insights for the future designing of the state-of-art theoretical methods. © 2016 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

The interpolation technique has shown many promises for simulating chemical dynamics with quantum chemical accuracy at molecular mechanics speed. This is achieved by constructing analytic potential energy surfaces with quantum chemical information at multiple conformational points, without assuming any functional form for the potentials. Here, we briefly review the course the method was developed over the past few decades, with a special focus on the activities in Korea. We also describe its strengths and weaknesses toward describing condensed phase chemical dynamics with the present implementations. Perspectives for future developments toward increasing applicability are discussed as concluding remarks. © 2015 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Dissociative adsorption of molecular oxygen (O2) on aluminum (Al) clusters has attracted much interest in the field of surface science and catalysis, but theoretical predictions of the reactivity of this reaction in terms of barrier height is still challenging. In this regard, we systematically investigate the reactivity of O2 with Al clusters using density functional theory (DFT) and atom-centered density matrix propagation (ADMP) simulations. We also calculate potential energy surfaces (PESs) of the reaction between O2 and Al clusters to estimate the barrier energy of this reaction. The M06-2X functional gives the barrier energy in agreement with the one calculated by coupled cluster singles and doubles with perturbed triples (CCSD(T)) while the TPSSh functional significantly underestimates the barrier height. The ADMP simulation using the M06-2X functional predicts the reactivity of O2 with the Al cluster in agreement with the experimental findings, that is, singlet O2 readily reacts with Al clusters but triplet O2 is less reactive. We found that the ability of a DFT functional to describe the charge transfer appropriately is critical for calculating the barrier energy and the reactivity of the reaction of O2 with Al clusters. The M06-2X functional is relevant for investigating chemical reactions involving Al and O2. © 2016 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

A full dimensional time-dependent quantum wavepacket approach is used to study the photodissociation dynamics of nitrous oxide for the X [ABSTRACT FROM AUTHOR]

The ring opening of cyclobutene is characterized by a competition of the two different pathways: a usual pathway over a saddle of index one (SP1) along the conrotatory behavior of the end groups, as well as a 'forbidden' pathway over a saddle point of index two (SP2) along the disrotatory behavior of the end CH2 groups. We use the system of ordinary differential equations for the method of the gentlest ascent dynamics (GAD) to determine saddle points of the potential energy surface (PES) of the ring opening of cyclobutene to cis-butadiene. We apply generalized GAD formulas for the search of a saddle point of index two. To understand the relation of the different regions of the PES (around minimums, around SPs of index one or two) we also calculate valley-ridge inflection (VRI) points on the PES using Newton trajectories (NT). VRIs and the corresponding singular NTs subdivide the regions of 'attraction' of the different SPs. We calculate the connections of the SP2 (in its different symmetry versions) with different SPs of index one of the PES by different 'reaction pathways.' We compare the possibilities of the tool of the GAD curves for the exploration of PESs with these of NT. The barrier of the disrotatory SP2 is somewhat higher than the barrier of the conrotatory SP1, however, pathways across the slope to the SP2 open additional reaction valleys. © 2015 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Development and applications of neural network (NN)-based approaches for representing potential energy surfaces (PES) of bound and reactive molecular systems are reviewed. Specifically, it is shown that when the density of ab initio points is low, NNs-based potentials with multibody or multimode structure are advantageous for representing high-dimensional PESs. Importantly, with an appropriate choice of the neuron activation function, PESs in the sum-of-products form are naturally obtained, thus addressing a bottleneck problem in quantum dynamics. The use of NN committees is also analyzed and it is shown that while they are able to reduce the fitting error, the reduction is limited by the nonrandom nature of the fitting error. The approaches described here are expected to be directly applicable in other areas of science and engineering where a functional form needs to be constructed in an unbiased way from sparse data. © 2014 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

The title reaction has a great deal of intriguing characters and provides energy for a chemical laser, and of much theoretical and experimental interest. Accurate description of the F + H2 → HF + H and F + HD → HF/DF + D/H reaction within the Born-Oppenheimer approximation presents a great challenge to the capabilities of modern quantum chemistry methods. The FHH system, which has strongly coupled eleven electrons, requires elaborate quantum chemistry calculations in the determination of potential energies with high accuracy. Moreover, a quantum reaction dynamics calculation for the F + H2/HD reaction requires much computational effort due to its large exothermicity. After more than half a century's endeavor, now we are capable of describing the F + H2/HD reaction close to spectroscopic accuracy. In this article, a brief review of the development of the potential energy surfaces and quantum reaction dynamics of the title reaction and its isotope substitutes is presented. Some of the results by quantum reactive scattering theory using the latest several typical potential energy surfaces are given, along with the corresponding experimental measurements, to illustrate the current stage of our capability on describing the F + H2/HD reaction. © 2015 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Much progress has been achieved in the developments of accurate and efficient algorithms for quantum dynamics calculations in the past two decades. Based on the reliable potential energy surfaces (PESs) constructed with state-of-the-art ab initio calculations, quantum reactive scattering calculations for the atom-diatom collisions can be performed accurately at the state-to-state level. In this review, we described the general strategies of constructing a PES and the Chebyshev real wave packet method briefly, and summarized our recent studies on the PESs and state-to-state reaction dynamics for the reactions of the atom N with radicals OH, CH, and C2. Such barrierless complex-forming reactions are very important for understanding low-temperature reaction dynamics and still difficult to treat accurately. © 2014 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

The idea of a macroscopic Andronikashvili experiment used to measure superfluid fraction of bulk liquid 4He can be ported into the realm of spectroscopic studies to measure the superfluid fraction of microscopic systems at the nanoscale. Theoretical studies are needed to fully unravel the superfluid information contained in such a microscopic Andronikashvili experiment. Two aspects of the theoretical studies, the generation of accurate and efficient potential energy surfaces, and the methodology of path-integral Monte Carlo simulations are briefly introduced in this article. © 2014 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

The bond-stretch isomers are characterized by a principal change in the bond-length with the rest of the molecule being unaltered. The electronic structure regulates the bond stretch isomerism phenomenon in [ABSTRACT FROM AUTHOR]

The intrinsic reaction coordinate (IRC) approach has been used extensively in quantum chemical analysis and prediction of the mechanism of chemical reactions. The IRC gives a unique connection from a given transition structure to local minima of the reactant and product sides. This allows for easy understanding of complicated multistep mechanisms as a set of simple elementary reaction steps. In this article, three topics concerning the IRC approach are discussed. In the first topic, the first ab initio study of the IRC and a recent development of an IRC calculation algorithm for enzyme reactions are introduced. In the second topic, cases are presented in which dynamical trajectories bifurcate and corresponding IRC connections can be inaccurate. In the third topic, a recent development of an automated reaction path search method and its application to systematic construction of IRC networks are described. Finally, combining these three topics, future perspectives are discussed. © 2014 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Density functional theory method is used to examine a series of group III triazides X(N3)3 (X = B, Al, Ga). These compounds, except for the C3 h planar B(N3)3 and Al(N3)3, are first reported here. C3 h planar structures are the most energetically favored for all singlet X(N3)3 systems. Potential-energy surfaces for unimolecular decompositions of the C3 h and CS planar X(N3)3 species have been investigated. Results show that decomposition of B(N3)3 obeys sequential fashion and follows a four-step mechanism: (1) B(N3)3 → NB(N3)2 + N2; (2) NB(N3)2 → cyc-N2BN3 + N2; (3) cyc-N2BN3 → trigonal-BN3 + N2; (4) trigonal-BN3 → linear-NBNN. Decomposition of Al(N3)3 follows a two-step mechanism: (1) Al(N3)3 → NAl(N3)2 + N2; (2) NAl(N3)2 → linear-AlN3 + 2N2. The dissociation of Ga(N3)3 follows only one-step mechanism: Ga(N3)3 → angular-GaN3 + 3N2. These findings may be helpful in understanding the decomposition mechanisms of group III triazides as well as the possible mechanism for XN film generation. © 2014 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

We investigate the possible locality of potential energy surface (PES) coupling in curvilinear internal valence coordinates using pure electronic energy as well as vibrational energy guided definitions of PES coupling range on the example of the floppy but-enal and the semirigid but-dienol molecule C4OH6. We propose ways to exploit found coupling range limits for efficient PES generation leading to significant computational savings. The generation of the 27 dimensional PESs using vibrationally guided convergence criteria within an adaptive PES generation method (AGAPES) at B3LYP quality is reported as well with a detailed error-gain analysis. © 2014 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

The structures, stabilities, nature of bonding, and potential energy surfaces of low-energy isomers of planar C nB5 ( n = 1−7) have been systematically explored at the CCSD(T)/6-311+G(d)//B3LYP/6-311+G(d) level. Incremental binding energy (IBE) and second order energy difference (Δ2 E) analyses demonstrate that C nB5 clusters with even n have relatively higher stability. The nature of bonding in these clusters is discussed based on valence molecular orbital (VMO), and Mayer bond order (MBO). Hückel (4 n + 2) rule and nucleus-independent chemical shift (NICS) values suggest that the ground states of C3B5, C4B5, and C7B5 have π aromaticity. VMO, electron localization function (ELF), adaptive natural density partitioning (AdNDP), and NICS analyses reveal the double aromaticity of C3B5 cation. CB5 and C3B5 are stable both thermodynamically and kinetically based on isomerization analysis. In addition, the simulated IR spectra are expected to be helpful for future experimental studies of these clusters. [ABSTRACT FROM AUTHOR]

We perform a systematic study on the geometry, stability, nature of bonding, and potential energy surface of low-lying isomers of planar and cyclic B nN2 ( n = 1−6) at the CCSD(T)/6-311+G(d)//B3LYP/6-311+G(d) level. B nN2 ( n = 2−4) clusters are structurally similar to pure boron clusters. The evolution of the binding energy per atom, incremental binding energy, and second-order difference of total energy with the size of B nN2 reveals that the lowest energy isomer of B3N2 has high stability. B5N2 and B6N2 possess π-aromaticity according to Hückel (4 n + 2) rule. The aromaticity of some isomers of B4N2 and B6N2 is examined based on their valence molecular orbitals. At the CCSD(T)/6-311+G(d)//B3LYP/6-311+G(d) level, several B2N2, B3N2, B4N2, and B5N2 isomers are predicted to be stable both thermodynamically and kinetically, and detectable in future experiments. © 2013 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

A global potential energy surface (PES) for the H [ABSTRACT FROM AUTHOR]

Potential energy surface (PES) for 1-styrylnaphthalene was calculated by PM3 method for the S0 state and PM3-CI(2x2) method with configuration interaction for the S1 state. Scanning PES along both isomerization and cyclization reaction coordinates enabled to reveal the minimum energy path (MEP) with low barriers on the S1 PES from E-isomer to dihydrocyclophotoproduct (DHP). This is consistent with formation of the photocyclization product in one-photon process during irradiation of E-isomer. Additionally, the MEP was found to bypass the coordinate region of Z-isomer, i.e. one-photon E-isomer-to-DHP photocyclization does not demand participation of the excited Z-isomer. Therefore, adiabatic trans-to-cis isomerization is likely not an intermediate stage on the E-isomer photocyclization pathway, and experimentally observed one-photon formation of the DHP from the E-isomer is likely not an evidence for adiabatic trans-to-cis photoisomerization, as it is usually assumed. According to the results obtained, two photochemical reactions of E-isomer, photoisomerization to Z-isomer and photocyclization to DHP, are not consecutive but parallel reactions with branching at perpendicular conformer on the S1 PES. © 2012 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

We present for the first time an analytical potential energy surface (PES) for the reaction of hydrogen abstraction from ammonia by a chlorine atom. It has a very complicated shape with various maxima and minima. The functional form used in the development of the PES considered the stretching and bending nuclear motions, and the parameters in the calibration process were fitted to reproduce exclusively high-level ab initio electronic structure calculations obtained at the CCSD(T) = FULL/aug-cc-pVTZ//CCSD(T) = FC/cc-pVTZ single point level. Thus, the surface is completely symmetric with respect to the permutation of the three ammonia hydrogen atoms, and no experimental information is used in the process. The ab initio information used in the fit includes a wide spectrum of properties (equilibrium geometries, relative energies, and vibrational frequencies) of the reactants, products, saddle point, intermediate complexes in the entry and exit channels, points on the reaction path, and points on the reaction swath. By comparison with the reference results, we show that the resulting PES reproduces not only the ab initio data used in the fitting procedure but also other thermochemical and kinetics results computed at the same ab initio level, which were not used in the fit-equilibrium constants, rate constants, and kinetic isotope effects. This represents a severe test for the new surface. As a first application, we perform an extensive kinetics study using variational transition-state theory with semiclassical transmission coefficients over a wide temperature range, 200-2000 K, on this analytical PES. The forward rate constants reproduce the sparse experimental measurements, while the reverse ones reproduce the change of activation energy with temperature reported in another theoretical study, although unfortunately there are no experimental data for comparison. Finally, we analyze the influence of the intermediate complexes and the spin-orbit correction on the kinetics results. In summary, these results indicate that the PES adequately describes this reaction, and the reasonable agreement with experiment lends further confidence to this new surface. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011 [ABSTRACT FROM AUTHOR]

An in-depth theoretical study is carried out at the B3LYP/6-311G(d,p), M062X/aug- cc-pVDZ and CCSD(T)/6-311++G(3df,2dp) (single-point) levels as an attempt to explore the mechanism of the little-understood ion-molecule reaction between NH+ and CH2O. Various possible reaction pathways are taken into account. It is shown that six dissociation products, including P 1 (2N + CH2OH+), P 2 (4N + CH2OH+), P 3 (3NH + CH2O+), P 4 (NH2 + HCO+), P 5 (NH [ABSTRACT FROM AUTHOR]

Boron and mixed-boron clusters have received considerable attention because of their wide applications and their essential roles in advancing chemical bonding models. Bearing the bright prospects as building blocks to form novel polymeric materials, the sulfur-rich boron sulfides have been greatly studied. However, the knowledge of the boron-rich boron sulfides is much rare. In this article, we report an extensive theoretical study on the structural, energetic, and stability features of a hitherto unknown septa-atomic cluster B6S at the CCSD(T)/6-311+G(2df)//B3LYP/6-311+G(d) level. The local minimum isomers were obtained through our recently developed program 'grid-based comprehensive isomeric search algorithm.' The results show that the planar knife-like isomer B5(−BS) 01 (0.0 kcal/mol) containing the −BS moiety is the lowest energy, followed by the quasi-planar belt-like isomer B6(>S) 02 (6.7 kcal/mol) and the pyramid-like isomer B6(>S) 03 (8.4 kcal/mol). Notably, the three singlet isomers all have good kinetic stability on the basis of the potential energy surface analysis. The B/S-centered wheel-like isomers are unfavorable in thermodynamics and kinetics. The triplet state structures generally can not compete with the singlet ones. The results are compared to the analogous and isoelectronic cluster B6O. Our work is expected to provide useful information for understanding the structures and stability of boron sulfides. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012 [ABSTRACT FROM AUTHOR]

The potential energy surface for sarin (C4H10FO2P) dissociation into (CH3)2CHO+PO(F)(CH3), CH3+(CH3)2CHOPO(F), and F+(CH3)2CHOPO(CH3) in the T1 and S1 states were investigated at the complete-active-space self-consistent field (CASSCF) with the 6-31G** and aug-cc-PVDZ basis sets. The different reaction pathways are characterized on the basis of the computed potential energy surface and surface crossing point, the time-dependent density functional theory (TD-DFT) was used to calculate the vertical energies based on the CAS(8,7)/6-31G** optimized excited structures, which may provide some new insights into the mechanism of the ultraviolet photo-degradation of sarin molecules. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011 [ABSTRACT FROM AUTHOR]

The mechanism of the cycloaddition reaction between singlet dimethyl-silylene carbene and formaldehyde has been investigated with MP2/6-31G* method, including geometry optimization and vibrational analysis for the involved stationary points on the potential energy surface. The energies of the different conformations are calculated by zero-point energy and CCSD (T)//MP2/6-31G* method. From the potential energy profile, it can be predicted that the reaction has two competitive dominant reaction pathways. The main products of first dominant reaction pathway are a planar four-membered ring product (P4) and its H-transfer product (P4.2). The main product of second dominant reaction pathway is a silicic bis-heterocyclic compound (P5). © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011 [ABSTRACT FROM AUTHOR]

The mechanism of the sulfur extraction reaction between singlet germylene carbene and its derivatives [X2GeC: (X = H, F, Cl, CH3)] and thiirane has been investigated with density functional theory, including geometry optimization and vibrational analyses for the involved stationary points on the potential energy surface. The energies of the different conformations are calculated by B3LYP/6‐311G(d,p) method. From the potential energy profile, it can be predicted that the reaction pathway of this kind consists two steps: (1) the two reactants firstly form an intermediate (INT) through a barrier‐free exothermic reaction; (2) the INT then isomerizes to a product via a transition state (TS). This kind reaction has similar mechanism, when the germylene carbene and its derivatives [X2GeC: (X = H, F, Cl, CH3)] and thiirane get close to each other, the shift of 3p lone electron pair of S in thiirane to the 2p unoccupied orbital of C in X2Ge = C: gives a p → p donor–acceptor bond, leading to the formation of INT. As the p → p donor–acceptor bond continues to strengthen (that is the CS bond continues to shorten), the INT generates product (P + C2H4) via TS. It is the substituent electronegativity that mainly affects the extraction reactions. When the substituent electronegativity is greater, the energy barrier is lower, and the reaction rate is greater. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011 [ABSTRACT FROM AUTHOR]

Density functional theory calculations have been performed to explore the potential energy surfaces of CO bond activation in CO2 molecule by gas‐phase Nb atom and Nb+ cation for better understanding the reaction mechanism of second‐row metal with CO2. The minimum‐energy reaction path is found to involve the spin inversion in the different reaction steps. This potential energy curve‐crossing dramatically affects the reaction energetic. The present results show that the mechanism is insertion‐elimination mechanism along the CO bond activation reaction. All theoretical results not only support the existing conclusions inferred from early experiment but also complement the pathway and mechanism for this reaction. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011 [ABSTRACT FROM AUTHOR]

The mechanism of the oxide extraction reaction between singlet silylene carbene and its derivatives [XSi = C: (X = H, F, Cl, CH)] and ethylene oxide has been investigated with density functional theory, including geometry optimization and vibrational analysis for the involved stationary points on the potential energy surface. The energies of the different conformations are calculated by B3LYP/6-311G(d,p) method. From the potential energy profile, it can be predicted that the reaction pathway of this kind consists two steps, the first step is the two reactants firstly form an intermediate (INT) through a barrier-free exothermic reaction; the second step is the INT then generates a product via a transition state (TS). This kind reaction has similar mechanism, when the silylene carbene and its derivatives [XSi = C: (X = H, F, Cl, CH)] and ethylene oxide close to each other, the shift of 2p lone electron pair of O in ethylene oxide to the 2p unoccupied orbital of C in XSi = C: gives a p → p donor-acceptor bond, thereby leading to the formation of INT. As the p → p donor-acceptor bond continues to strengthen (that is, the CO bond continues to shorten), the INT generates product (P + CH) via TS. It is the substituent electronegativity, which mainly affects the extraction reactions. When the substituent electronegativity is greater, the energy barrier is lower, and the reaction rate is greater. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011 [ABSTRACT FROM AUTHOR]

The mechanism of the cycloaddition reaction between singlet dichloro-germylene carbene and aldehyde has been investigated with MP2/6-31G* method, including geometry optimization and vibrational analysis for the involved stationary points on the potential energy surface. The energies of the different conformations are calculated by zero-point energy and CCSD (T)//MP2/6-31G* method. From the potential energy profile, it can be predicted that the reaction has two competitive dominant reaction pathways. The channel (A) consists of four steps: (1) the two reactants (R1, R2) first form an intermediate INT2 through a barrier-free exothermic reaction of 142.4 kJ/mol; (2) INT2 then isomerizes to a four-membered ring compound P2 via a transition state TS2 with energy barrier of 8.4 kJ/mol; (3) P2 further reacts with aldehyde (R2) to form an intermediate INT3, which is also a barrier-free exothermic reaction of 9.2 kJ/mol; (4) INT3 isomerizes to a germanic bis-heterocyclic product P3 via a transition state TS3 with energy barrier of 4.5 kJ/mol. The process of channel (B) is as follows: (1) the two reactants (R1, R2) first form an intermediate INT4 through a barrier-free exothermic reaction of 251.5 kJ/mol; (2) INT4 further reacts with aldehyde (R2) to form an intermediate INT5, which is also a barrier-free exothermic reaction of 173.5 kJ/mol; (3) INT5 then isomerizes to a germanic bis-heterocyclic product P5 via a transition state TS5 with an energy barrier of 69.4 kJ/mol. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011 [ABSTRACT FROM AUTHOR]

The intermediates [Si,O,C,O] of the Si + CO reaction have been studied in detail using high level ab iniitio methods. Both singlet and triplet [Si,O,C,O] species are characterized structurally and energetically. On the singlet potential energy surface (PES), the vdw-OSi-CO isomer and in the triplet PES, the bent-SiOCO isomer is found to be thermodynamically as well as kinetically most stable species. All possible isomerization transition states (TS) are located on both singlet and triplet potential surfaces. On the triplet surface, the stability of the trans-OSiCO isomer is comparable with that of the bent-SiOCO isomer. A non-planar cis-SiOCO isomer is located on the triplet PES, which is predicted for the first time. Heats of formation at 0 K (Δ H°, 0 K) for all singlet and triplet species are computed using G3B3, G3MP2, and CBS-Q theories. The discrepancy between G3B3 and the other two methods for the heat of formation value for triplet trans-OSiCO is discussed. The PESs for singlet as well as triplet species with their dissociation asymptotes are explored at the CCSD(T)/6-311G(d,p)//MP2/6-311G(d,p) level of theory. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2011 [ABSTRACT FROM AUTHOR]

The mechanisms for the reaction of CHSSCH with OH radical are investigated at the QCISD(T)/6-311++G(d,p)//B3LYP/6-311++G(d,p) level of theory. Five channels have been obtained and six transition state structures have been located for the title reaction. The initial association between CHSSCH and OH, which forms two low-energy adducts named as CHS(OH)SCH (IM1 and IM2), is confirmed to be a barrierless process, The SS bond rupture and HS bond formation of IM1 lead to the products P1(CHSH + CHSO) with a barrier height of 40.00 kJ mol. The reaction energy of Path 1 is −74.04 kJ mol. P1 is the most abundant in view of both thermodynamics and dynamics. In addition, IMs can lead to the products P2 (CHS + CHSOH), P3 (HO + CHS + CHS), P4 (CH + CHSSOH), and P5 (CH + CHSSO) by addition-elimination or hydrogen abstraction mechanism. All products are thermodynamically favorable except for P4 (CH + CHSSOH). The reaction energies of Path 2, Path 3, Path 4, and Path 5 are −28.42, −46.90, 28.03, and −89.47 kJ mol, respectively. Path 5 is the least favorable channel despite its largest exothermicity (−89.47 kJ mol) because this process must undergo two barriers of TS5 (109.0 kJ mol) and TS6 (25.49 kJ mol). Hopefully, the results presented in this study may provide helpful information on deep insight into the reaction mechanism. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2011 [ABSTRACT FROM AUTHOR]

The potential energy surface of O(D) + CHCHBr reaction has been studied using QCISD(T)/6-311++G(d,p)//MP2/6-311G(d,p) method. The calculations reveal an insertion-elimination reaction mechanism of the title reaction. The insertion process has two possibilities: one is the O(D) inserting into CBr bond of CHCHBr producing one energy-rich intermediate CHCHOBr and another is the O(D) inserting into one of the CH bonds of CHCHBr producing two energy-rich intermediates, IM1 and IM2. The three intermediates subsequently decompose to various products. The calculations of the branching ratios of various products formed though the three intermediates have been carried out using RRKM theory at the collision energies of 0, 5, 10, 15, 20, 25, and 30 kcal/mol. CHCHO + Br are the main decomposition products of CHCHOBr. CHCOH + HBr and CHCHOH + HBr are the main decomposition products for IM1; CHCHOH + HBr are the main decomposition products for IM2. As IM1 is more stable and more likely to form than CHCHOBr and IM2, CHCOH + HBr and CHCHOH + HBr are probably the main products of the O(D) + CHCHBr reaction. Our computational results can give insight into reaction mechanism and provide probable explanations for future experiments. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2011 [ABSTRACT FROM AUTHOR]

A theoretical study of the potential energy surface (PES) for the decomposition of the i-CH cation has been done at RHF/MP2 level. In a previous study on the Li + i-CHCl system under single collision conditions, the authors measured the cross section energy dependence for the formation of this cation and its decomposition in CH + CH. Theoretical calculations on the PES of the CH system have provided reaction paths for both, its decomposition channel and its isomerization to n-CH. The former reaction path involves a large increase of one CC bond length of the initial ion, nearly forming a CH neutral fragment that, by interacting with the remaining fragment, abstracts a hydrogen atom, giving methane and CH as final products. The energy requirement for this reaction is given by the process endoergicity, without any additional potential barrier. For the isomerization reaction, a transition state has been located between both potential wells, with the corresponding reaction path fully characterized by the IRC method. The main features of the calculated PES allow us to interpret, at least qualitatively, the experimental data previously obtained in our group. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011 [ABSTRACT FROM AUTHOR]

Ab initio electronic structure methods have reached a satisfactory accuracy for the calculation of static properties, but remain too expensive for quantum dynamical calculations. Recently, an efficient semiclassical method was proposed to evaluate the accuracy of quantum dynamics on an approximate potential without having to perform the expensive quantum dynamics on the accurate potential. Here, this method is applied for the first time to evaluate the accuracy of quantum dynamics on an approximate analytical or interpolated potential in comparison to the quantum dynamics on an accurate potential obtained by an ab initio electronic structure method. Specifically, the vibrational dynamics of H2 on a Morse potential is compared with that on the full CI potential, and the photodissociation dynamics of CO2 on a LEPS potential with that on the excited 1Π surface computed at the EOM-CCSD/aug-cc-pVDZ level of theory. Finally, the effect of discretization of a potential energy surface on the quantum dynamics is evaluated. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 [ABSTRACT FROM AUTHOR]

The mechanism of the cycloaddition reaction of forming a silapolycyclic compound between singlet methylenesilylene and acetone has been investigated with MP2/6-31G* method, including geometry optimization and vibrational analysis for the involved stationary points on the potential energy surface. The energies of the different conformations are calculated by CCSD(T)//MP2/6-31G* method. From the potential energy profile, we predict that the cycloaddition reaction of forming a silapolycyclic compound between singlet methylenesilylene and acetone has two competitive dominant reaction pathways. First dominant reaction pathway consists of four steps: (I) the two reactants (R1, R2) first form an intermediate (INT1) through a barrier-free exothermic reaction of 46.2 kJ/mol; (II) intermediate (INT1) then isomerizes to a planar four-membered ring product (P3) via transition state (TS3) with an energy barrier of 47.1 kJ/mol; (III) planar four-membered ring product (P3) further reacts with acetone (R2) to form an intermediate (INT4), which is also a barrier-free exothermic reaction of 40.0 kJ/mol; (IV) intermediate (INT4) isomerizes to a silapolycyclic compound (P4) via transition state (TS4) with an energy barrier of 57.0 kJ/mol. Second dominant reaction pathway consists of three steps: (I) the two reactants (R1, R2) first form a four-membered ring intermediate (INT2) through a barrier-free exothermic reaction of 0.5 kJ/mol; (II) INT2 further reacts with acetone (R2) to form an intermediate (INT5), which is also a barrier-free exothermic reaction of 45.4 kJ/mol; (III) intermediate (INT5) isomerizes to a silapolycyclic compound (P5) via transition state (TS5) with an energy barrier of 49.3 kJ/mol. P4 and P5 are isomeric compounds. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 [ABSTRACT FROM AUTHOR]

The lowest doublet electronic state for the lithium trimer (12A′) is calculated for use in three-body scattering calculations using the valence electron FCI method with atomic cores represented using an effective core potential. It is shown that an accurate description of core-valence correlation is necessary for accurate calculations of molecular bond lengths, frequencies and dissociation energies. Interpolation between 12A′ ab initio surface data points in a sparse grid is done using the global interpolant moving least squares method with a smooth radial data cutoff function included in the fitting weights and bivariate polynomials as a basis set. The Jahn–Teller splitting of the 12E′ surface into the 12A1 and 12B2 states is investigated using a combination of both CASSCF and FCI levels of theory. Additionally, preliminary calculations of the 12A″ surface are also presented using second order spin restricted open-shell Møller–Plesset perturbation level of theory. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [ABSTRACT FROM AUTHOR]

We explored the possibilities of proton-transfer reactions between guanines (G) and cytosines (C) in stacking two GC pairs by means of density functional methods. There are two combinations of sequences, GC/GC (5′-dGpG-3′) and CG/GC (5′-dCpG-3′). We found that the simultaneous single proton transfer (SPT) in two base pairs, two independent double proton transfer (DPT), and continuous double SPT reactions strongly depend on the sequence of the DNA, because the SPT reaction occurs in specific sequences including CG/GC and the latter DPTs occur in those including GC/GC. The properties of the DPT products, such as effective charges, are almost the same as the original GC/GC, whereas the effective charges on G and C in the simultaneous SPT product become negative and positive in comparison with those in the original GC/GC. Coulomb attraction caused by the charge separation mainly contributes to the stability of the SPT product. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [ABSTRACT FROM AUTHOR]