Accurate Double Many-body Expansion Research Articles

Quasiclassical Trajectory Study of the Si + SH Reaction on an Accurate Double Many-Body Expansion Potential Energy Surface

An accurate potential energy surface (PES) for the HSiS system based on MRCI+Q calculations extrapolated to the complete basis set limit is presented. Modeled with the double many-body expansion (DMBE) method, the PES provides an accurate description of the long-range interactions, including electrostatic and dispersion terms decaying as R-4, R-5, R-6, R-8, R-10 that are predicted from dipole moments, quadrupole moments, and dipolar polarizabilities, which are also calculated at the MRCI+Q level. The novel PES is then used in quasiclassical trajectory calculations to predict the rate coefficients of the Si + SH → SiS + H reaction, which has been shown to be a major source of the SiS in certain regions of the interstellar medium. An account of the zero-point energy leakage based on various nonactive models is also given. It is shown that the reaction is dominated by long-range forces, with the mechanism Si + SH → SiSH → SSiH → SiS + H being the most important one for all temperatures studied. Although SSiH corresponds to the global minimum of the PES, the contribution from the direct reaction Si + SH → SSiH → SiS + H is less than 0.5% for temperatures higher than 500 K. The rovibrational distributions of the products are calculated using the momentum Gaussian binning method and show that as the temperature is increased the average vibrational quantum number decreases while the rotational distribution spreads up to larger values.

Theoretical insight into the effect of collision energy on the S(3P) + SH(X2∏) → S2(X3∑g−) + H(2S) reaction

In this work, the dynamics of reaction S(3P) + SH(X2∏) → S2(X3∑g−) + H(2S) has been investigated using quasi-classical trajectories method on a newly constructed accurate double many-body expansion potential energy surface of Song et al. [J. Phys. Chem. A 115, 5274 (2011)]. The integral cross section and the rate constant are obtained. Furthermore, the distribution reflecting vector correlation and the polarization-dependent differential cross section are investigated. The results show a decreasing behavior of the integral cross section as the increasing of the collision energy, and dominate complex forming mechanism at lower energies, as well as the stripping mechanism at higher energies. Those results indicate that the product S2 is sensitively affected by the collision energy.

Accurate double many-body expansion potential energy surface of HS2A2A′) by scaling the external correlation**Project supported by the National Natural Science Foundation of China (Grant No. 11304185), the Taishan Scholar Project of Shandong Province, China, the Shandong Provincial Natural Science Foundation, China (Grant No. ZR2014AM022), the Shandong Province Higher Educational Science and Technology Program, China (Grant No. J15LJ03), the China Postdoctoral

A globally accurate single-sheeted double many-body expansion potential energy surface is reported for the first excited state of HS2 by fitting the accurate ab initio energies, which are calculated at the multireference configuration interaction level with the aug-cc-pVQZ basis set. By using the double many-body expansion-scaled external correlation method, such calculated ab initio energies are then slightly corrected by scaling their dynamical correlation. A grid of 2767 ab initio energies is used in the least-square fitting procedure with the total root-mean square deviation being 1.406 kcal·mol−1. The topographical features of the HS2(A2A′) global potential energy surface are examined in detail. The attributes of the stationary points are presented and compared with the corresponding ab initio results as well as experimental and other theoretical data, showing good agreement. The resulting potential energy surface of HS2(A2A′) can be used as a building block for constructing the global potential energy surfaces of larger S/H molecular systems and recommended for dynamic studies on the title molecular system.

Accurate double many-body expansion potential energy surface for the 2(1)A' state of N2O.

An accurate double many-body expansion potential energy surface is reported for the 2(1)A' state of N2O. The new double many-body expansion (DMBE) form has been fitted to a wealth of ab initio points that have been calculated at the multi-reference configuration interaction level using the full-valence-complete-active-space wave function as reference and the cc-pVQZ basis set, and subsequently corrected semiempirically via double many-body expansion-scaled external correlation method to extrapolate the calculated energies to the limit of a complete basis set and, most importantly, the limit of an infinite configuration interaction expansion. The topographical features of the novel potential energy surface are then examined in detail and compared with corresponding attributes of other potential functions available in the literature. Exploratory trajectories have also been run on this DMBE form with the quasiclassical trajectory method, with the thermal rate constant so determined at room temperature significantly enhancing agreement with experimental data.

A typical slow reaction H(2S) + S2(X3Σ−g) → SH(X2Π) + S(3P) on a new surface: Quantum dynamics calculations

Quantum dynamics calculations for the title reaction H(2S) + S2(X3Σ−g) → SH(X2Π) + S(3P) are performed by using a globally accurate double many-body expansion potential energy surface [J. Phys. Chem. A 115 5274 (2011)]. The Chebyshev real wave packet propagation method is employed to obtain the dynamical information, such as reaction probability, initial state-specified integral cross section, and thermal rate constant. It is found not only that there is a reaction threshold near 0.7 eV in both reaction probabilities and integral cross section curves, but also that both the probability and cross section increase firstly and then decrease as the collision energy increases. The existence of the resonance structure in both the probability and cross section curves is ascribed to the deep potential well. The calculation of the rate constant reveals that the reaction occurring on the potential energy surface of the ground-state HS2 is slow to take place.

Accurate double many-body expansion potential energy surface by extrapolation to the complete basis set limit and dynamics calculations for ground state of NH2

An accurate single-sheeted double many-body expansion potential energy surface is reported for the title system. A switching function formalism has been used to warrant the correct behavior at the H2(X1Σg+)+N(2D) and NH (X3Σ-)+H(2S) dissociation channels involving nitrogen in the ground N(4S) and first excited N(2D) states. The topographical features of the novel global potential energy surface are examined in detail, and found to be in good agreement with those calculated directly from the raw ab initio energies, as well as previous calculations available in the literature. The novel surface can be using to treat well the Renner-Teller degeneracy of the 12A″ and 12A' states of NH 2. Such a work can both be recommended for dynamics studies of the N(2D)+H2 reaction and as building blocks for constructing the double many-body expansion potential energy surface of larger nitrogen/hydrogen-containing systems. In turn, a test theoretical study of the reaction N(2D)+H2(X1Σg+)(ν=0,j=0)→NH (X3Σ-)+H(2S) has been carried out with the method of quantum wave packet on the new potential energy surface. Reaction probabilities, integral cross sections, and differential cross sections have been calculated. Threshold exists because of the energy barrier (68.5 meV) along the minimum energy path. On the curve of reaction probability for total angular momentum J = 0, there are two sharp peaks just above threshold. The value of integral cross section increases quickly from zero to maximum with the increase of collision energy, and then stays stable with small oscillations. The differential cross section result shows that the reaction is a typical forward and backward scatter in agreement with experimental measurement result.

On the role of dynamical barriers in barrierless reactions at low energies: S(1D) + H2

Reaction probabilities as a function of total angular momentum (opacity functions) and the resulting reaction cross sections for the collision of open shell S((1)D) atoms with para-hydrogen have been calculated in the kinetic energy range 0.09-10 meV (1-120 K). The quantum mechanical hyperspherical reactive scattering method and quasi-classical trajectory and statistical quasi-classical trajectory approaches were used. Two different ab initio potential energy surfaces (PESs) have been considered. The widely used reproducing kernel Hilbert space (RKHS) PES by Ho et al. [T.-S. Ho, T. Hollebeek, H. Rabitz, S. D. Chao, R. T. Skodje, A. S. Zyubin, and A. M. Mebel, J. Chem. Phys 116, 4124 (2002)] and the recently published accurate double many-body expansion (DMBE)/complete basis set (CBS) PES by Song and Varandas [Y. Z. Song and A. J. C. Varandas, J. Chem. Phys. 130, 134317 (2009)]. The calculations at low collision energies reveal very different dynamical behaviors on the two PESs. The reactivity on the RKHS PES is found to be considerably larger than that on the DMBE/CBS PES as a result of larger reaction probabilities at low total (here also orbital) angular momentum values and to opacity functions which extend to significantly larger total angular momentum values. The observed differences have their origin in two major distinct topographic features. Although both PESs are essentially barrierless for equilibrium H-H distances, when the H-H bond is compressed the DMBE/CBS PES gives rise to a dynamical barrier which limits the reactivity of the system. This barrier is completely absent in the RHKS PES. In addition, the latter PES exhibits a van der Walls well in the entrance channel which reduces the height of the centrifugal barrier and is able to support resonances. As a result, a significant larger cross section is found on this PES, with marked oscillations attributable to shape resonances and/or to the opening of partial wave contributions. The comparison of the results on both PESs is illustrative of the wealth of the dynamics at low collision energy. It is also illuminating about the difficulties encountered in modeling an all-purpose global potential energy surface.

Accurate Double Many-Body Expansion Potential Energy Surface for Ground-State HS2Based on ab Initio Data Extrapolated to the Complete Basis Set Limit

A double many-body expansion potential energy surface is reported for the electronic ground state of HS(2) by fitting accurate multireference configuration interaction energies calculated with aug-cc-pVTdZ and aug-cc-pVQdZ basis sets upon separate extrapolation of the complete-active-space self-consistent field and dynamical correlation components of the total energy to the complete basis set limit. The major topographical features of the potential energy surface are examined in detail, and the model function is used for thermalized calculations of the rate constants for the S + SH → H + S(2) reaction at 298 and 400 K. A value of (1.44 ± 0.06) × 10(-11) cm(3) s(-1) is obtained at 298 K, providing perhaps the most reliable estimate of the rate constant known thus far for such a reaction.

Accurate Double Many-Body Expansion Potential Energy Surface for the Lowest Singlet State of Methylene

ADVERTISEMENT RETURN TO ISSUEPREVAddition/CorrectionORIGINAL ARTICLEThis notice is a correctionAccurate Double Many-Body Expansion Potential Energy Surface for the Lowest Singlet State of MethyleneS. Joseph and A. J. C. Varandas*Cite this: J. Phys. Chem. A 2009, 113, 49, 13824Publication Date (Web):November 13, 2009Publication History Published online13 November 2009Published inissue 10 December 2009https://doi.org/10.1021/jp910270qCopyright © 2009 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views365Altmetric-Citations1LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (19 KB) Get e-AlertsSUBJECTS:Carbene compounds,Energy,Potential energy Get e-Alerts

Accurate Double Many-Body Expansion Potential Energy Surface for the Lowest Singlet State of Methylene

A single-sheeted double many-body expansion potential energy surface is reported for ground-state CH(2) by fitting accurate ab initio energies that have been semiempirically corrected by the double many-body-expansion scaled-external-correlation method. The energies of about 2500 geometries have been calculated using the multireference configuration interaction method, with the single diffusely corrected aug-cc-pVQZ basis set of Dunning and the full valence complete active space wave function as reference. The topographical features of the novel global potential energy surface are examined and compared with other potential energy surfaces.

Accurate DMBE Potential Energy Surface For the N(2D) + H2(1Σ g + ) Reaction Using an Improved Switching Function Formalism

A single-sheeted double many-body expansion (DMBE) potential energy surface is reported for the 1 2 A′′ state of NH2. To approximate its true multi-sheeted nature, a novel switching function that imposes the correct behavior at the H2(X 1Σ + )+ N(2 D) and NH(X 3Σ-) + H(2 S) dissociation limits has been suggested. The new DMBE form is shown to fit with high accuracy an extensive set of new ab initio points (calculated at the multi-reference configuration interaction level using the full valence complete active space as reference and aug-cc-pVQZ and aug-cc-pV5Z basis sets) that have been semiempirically corrected at the valence regions by scaling the n-body dynamical correlation terms such as to account for the finite basis set size and truncated configuration interaction expansion. A detailed study of the N(2 D) ... H2(X 1Σ + ) van der Waals region has also been carried out. These calculations predict a nearly free rigid-rotor with two shallow van der Waals wells of C 2v and C ∞ v symmetries. Such a result contrasts with previous cc-pVTZ calculations which predict a single T-shaped van der Waals structure. Except in the vicinity of the crossing seam, which is replaced by an avoided intersection, the fit shows the correct physical behavior over the entire configurational space. The topographical features of the new DMBE potential energy surface are examined in detail and compared with those of other potential functions available in the literature. Amongst such features, we highlight the barrier for linearization (11,802 cm-1) which is found to overestimate the most recent empirical spectroscopic estimate by only 28 cm-1. Additionally, the T-shaped N(2 D) ... H2 van der Waals minimum is predicted to have a well depth of 90 cm-1, being 11 cm-1 deeper than the C ∞ v minimum. The title DMBE form is therefore recommendable for dynamics studies of both non-reactive and reactive N(2 D)+H2 collisions.

Ro-Vibrational States of Triplet H2D+

We present rotational term values for J < or = 3 of the vibrational states with up to twofold excitation of H2D+ in the lowest electronic triplet state (a3sigma(u)+). The calculations were performed using the method of hyperspherical harmonics and our recent accurate double many-body expansion potential energy surface.

Dimensionality effects on transition state resonances for [formula omitted] and [formula omitted] reactive collisions

The transition state resonances of the title reactions have been studied on the accurate double many-body expansion (DMBE) potential energy surface for H3 using two-dimensional (2D) and three-dimensional (3D) time-dependent wave packet propagation methods. It is shown that the resonance energies are strongly associated with the vibrational threshold states of the molecular fragment obtained upon dissociation, both in the 2D and 3D calculations. However, although the two systems have the same threshold states, the resonance widths for the 2D D+HD collisions are found to be considerably narrower than for the 3D ones, while no such phenomenon is observed for H+DH. As a result, we have concluded that there is an apparent dimensional effect on the resonance widths of the heavy–light–heavy (HLH) reaction.

Quasi-ab initio dynamics: a test trajectory study of the H+H 2 reaction using energies and gradients based on scaling of the external correlation

We have carried out a test dynamics study of the prototype H+H 2 exchange reaction by running quasi-classical trajectories `on-the-fly' using ab initio correlated energies which have been previously corrected semiempirically by the double many-body expansion plus scaling of the external correlation method to account for size-limitations of the one-electron basis set and configuration interaction expansion. The method is general and gives results in agreement with conventional trajectory calculations carried out on the accurate double many-body expansion potential energy surface for H 3.

A detailed state-to-state low-energy dynamics study of the reaction O(3P)+OH(2Π)→O2(X̃ 3Σg−)+H(2S) using a quasiclassical trajectory–internal-energy quantum-mechanical-threshold method

The quasiclassical trajectory (QCT) method has been used for a detailed study of the state-to-state dynamics of the reaction O(3P) + OH(2Π)→O2(X̂33Σ−g) + H(2S) over the range of translational energies 0.125 ≤ Etr/kcal mol−1≤2.0, corresponding to the temperature range 40≤T/K≤680. A novel variant of this method insuring that trajectory calculations properly account for the zero-point energy of the diatomic molecules, the so-called quasiclassical trajectory–internal-energy quantum-mechanical-threshold method, is also suggested and applied to the title reaction. The most recent and accurate double many-body expansion potential-energy surface for the ground doublet state of the hydroperoxyl radical has been employed in all calculations. The computed reactive cross sections for initial quantum rotational states of OH varying from J=0 to J=10 (the vibrational quantum number is kept fixed at v=0) are shown to have a marked decreasing dependence on translational energy, thus suggesting that long-range forces play a major role on the dynamics of the O(3P) + OH(2Π) reaction. A comparison of the thermalized rate coefficients with the results of direct experimental measurements is shown to agree best with the data of Howard and Smith over the whole range of temperatures covered by experiment. It is also shown that nonstatistical recrossing effects are important for all translational energies and rotational states, while a nearly linear dependence is shown over the range of translational energies that have been studied. Finally, appropriate averaging over the initial conditions shows that the dependence on temperature of the calculated recrossing factor is in good agreement with the corresponding estimate from recent direct thermalized QCT calculations using the same potential-energy surface while fitting well by a recently proposed model for this recrossing factor.