Ab initio potential energy surface and anharmonic vibration spectrum of NF_(3)^(+)

Potential energy surfaces(PESs), vibrational frequencies, and infrared spectra are calculated for NF_(3)^(+) using ab initio calculations, based on UCCSD(T)/cc-p VTZ combined with vibrational configuration interaction(VCI). Based on an iterative algorithm, the surfaces(SURF) program adds automatic points to the lattice representation of the potential function, the one-dimensional and two-dimensional PESs are calculated after reaching a convergence threshold, finally the smooth image of the potential energy surface is fitted. The PESs accurately account for the interaction between the different modes, with the mode q_(6) symmetrical stretching vibrations having the greatest effect on the potential energy change of the whole system throughout the potential energy surface shift. The anharmonic frequencies are obtained when the VCI matrix is diagonalized. Fundamental frequencies, overtones, and combination bands of NF_(3)^(+) are calculated, which generate the degenerate phenomenon between their frequencies. Finally, the calculated anharmonic frequency is used to plot the infrared spectra.Modal antisymmetric stretching ν_(5) and symmetric stretching ν_(6) exhibit a phenomenon of large-intensity borrowing. This study can provide data to support the characterization in the laboratory.

Global Potential Energy Surface for the H＋CH4←→H2＋CH3 Reaction using Neural Networks

A globla potential energy surface （PES） for the H＋CH4←→H2＋CH3 reaction has been constructed using the neural networks method based on 47783 high level ab initio geometry points. Extensive quasi-classical trajectories and quantum scattering calculations were carried out to check the convergence of the PES. This PES, fully converged with respect to the fitting procedure and the number of ab initio points, has a very small fitting error, and is much faster on evaluation than the modified Shepard interpolating PES, representing the best available PES for this benchmark polyatomic system.

Theoretical Study on Dissociation Potential Energy Surface of Peroxynitric Acid

The lowest energy structures of peroxynitric acid have been studied with B3LYP/6-311＋ G（2d,2p） method. The potential energy surfaces （PES） along the O-N and O-O bonds have been scanned at CCSD（T）/aug-cc-pVDZ level, respectively. The calculated results show that on the O-N PES, the O3-N4 bond length of the loose transition state is 2.82A^° and the corresponding energy barrier is 25.6 kcal/mol, while on the O-O PES, the loose transition state with of O2-O3 bond length of 2.35A^° has the energy barrier of 37.4 kcal/mol. Thus the primary reaction path for peroxynitric acid is the dissociation into HO2 and NO2.

A Global ab initio Potential Energy Surface for F+H_(2)→HF+H

A global three dimensional potential energy surface for the F＋H2→HF＋H reaction has been developed by spline interpolation of about 15,000 symmetry-unique ab initio points, obtained from the multi-reference configuration interaction level with Davidson correction using the aug-cc-pV5Z basis set. In the entrance channel the spin-orbit coupling energy is also included.

Three-dimensional Potential Energy Surface and Bound States of the Ar2-Ne Complex

The first three-dimensional interaction potential energy surface （PES） of the Ar2-Ne complex is developed using the single and double excitation coupled cluster theory with noniterative treatment of triple excitations CCSD（T）. The aug-cc-pVQZ basis sets are employed for all atoms, including an additional （3s3p2d2flg） set of midpoint bond functions. The calculated single point energies are fitted to an analytic two-dimensional potential model at each of seven fixed rAr~ values. The seven model potentials are then used to construct the three- dimensional PES by interpolating along （r-re） using a sixth-order polynomial. The PES is used in the following rovibrational energy levels calculations. The comparisons of theoretical transition frequencies and spectroscopic constants with the experimental results are given.

Analysis of Potential Energy Surface for Butanone Isomerization

The potential energy surfaces for butanone isomerization have been investigated by density function theory calculation. Six main reaction pathways are confirmed using the intrinsic reaction coordinate method, and the corresponding isomerization products are 1-buten-2-ol, 2-buten-2-ol, butanal or 1-buten-l-ol, methyl 1-propenyl ether, methyl allyl ether, and ethyl vinyl ether, respectively. Among them, there are three pathways through butylene oxide, indicating butylene oxide is an important intermediate product during butanone isomer ization. The calculated vertical ionization energies of the reactant and its products are in a good agreement with the experimental values available. From the consideration for the relative energies Of transition states and the number of high-energy barriers we infer that the reaction pathway butanone-＊l-buten-2-ol---2-buten-2-oi is the most competitive. The obtained results are informative for future studies on isomerization of ketone molecules.

Accelerating the Construction of Neural Network Potential Energy Surfaces： A Fast Hybrid Training Algorithm

Machine learning approaches have been promising in constructing high-dimensional potential energy surfaces （PESs） for molecules and materials. Neural networks （NNs） are one of the most popular such tools because of its simplicity and efficiency. The training algorithm for NNs becomes essential to achieve a fast and accurate fit with numerous data. The Levenberg-Marquardt （LM） algorithm has been recognized as one of the fastest and robust algorithms to train medium sized NNs and widely applied in recent NN based high quality PESs. However, when the number of ab initio data becomes large, the efficiency of LM is limited, making the training time consuming. Extreme learning machine （ELM） is a recently proposed algorithm which determines the weights and biases of a single hidden layer NN by a linear solution and is thus extremely fast. It, however, does not produce sufficiently small fitting error because of its random nature. Taking advantages of both algorithms, we report a generalized hybrid algorithm in training multilayer NNs. Tests on H＋H2 and CH4＋Ni（111） systems demonstrate the much higher efficiency of this hybrid algorithm （ELM-LM） over the original LM. We expect that ELM-LM will find its widespread applications in building up high-dimensional NN based PESs.

Time-dependent Wave Packet Quantum Scattering Study of Reaction S（3p）＋H2→HS＋H on a New ab initio Potential Energy Surface 3A’

A new potential energy surface is presented for the triplet state 3At of the chemical reaction S（3P）＋H2 from a set of accurate ab initio data. The single point energies are computed using highly correlated complete active space self-consistent-field and multi-reference configuration interaction wave functions with a basis set of aug-cc-pV5Z. We have fitted the full set of energy values using many-body expansion method with an Aguado-Paniagua function. Based on the new potential energy surface, we carry out the time-dependent wave packet scattering calculations over the collision energy range of 0.8-2.2 eV. Both the centrifugalsudden approximation and Coriolis Coupling cross sections are obtained. In addition, the total reaction probabilities are calculated for the reactant H2 initially in the vibrational states v=0-3 （j=0）. It is found that initial vibrational excitation enhances the title reaction.

Adiabatic Potential Energy Surfaces and Photodissociation Mechanisms for Highly Excited States of H_(2)O

Full-dimensional adiabatic potential energy surfaces of the electronic ground state X and nine excited states A,I,B,C,D,D',D'',E' and F of H_(2)O molecule are developed at the level of internally contracted multireference configuration interaction with the Davidson correction.The potential energy surfaces are fitted by using Gaussian process regression combining permutation invariant polynomials.With a large selected active space and extra diffuse basis set to describe these Rydberg states,the calculated vertical excited energies and equilibrium geometries are in good agreement with the previous theoretical and experimental values.Compared with the well-investigated photodissociation of the first three low-lying states,both theoretical and experimental studies on higher states are still limited.In this work,we focus on all the three channels of the highly excited state,which are directly involved in the vacuum ultraviolet photodissociation of water.In particular,some conical intersections of D-E',E'-F,A-I and I-C states are clearly illustrated for the first time based on the newly developed potential energy surfaces(PESs).The nonadiabatic dissociation pathways for these excited states are discussed in detail,which may shed light on the photodissociation mechanisms for these highly excited states.

Vibrational Spectra and Potential Energy Surface for Electronic Ground State of Jet-Cooled Molecule S2O

The vibration states of transition molecule S2O, including both bending and stretching vibrations, are studied in the framework of dynamical symmetry groups . We get all the vibration spectra of S2O by fitting 22 spectra data with 10 parameters. The fitting rms of the Hamiltonian is 2.12 cm-1. With the parameters and Lie algebraic theory, we give the analytical expression of the potential energy surface, which helps us to calculate the dissociation energy and force constants of S2O in the electronic ground state.

Scattering Resonance States and Partial Potential Energy Surface of Reaction I+HI(v=0)→IH(v′=0) +I

The partial potential energy surface of the I ＋ HI →IH ＋ I reaction involving the translational and vibrational motions has been constructed at the QCISD（ T ）//MP4SDQ level with the pseudo potential method that is helpful to interpreting the scattering resonance states. The lifetimes of the scattering resonance states in the title reaction obtained from the partial potential energy surface are about 90-120 fs, which agrees with the result of high-resolved threshold photodetachment spectroscopy of anion IHI^- measured by Neumark.

The effect of the attractive well of the potential energy surface for Ne-HC1 on rotationally inelastic partial wave cross sections

An interaction potential of the Ne-HC1 van der Waals complex is obtained by utilizing the Huxley analytic potential function to fit the accurate interaction energy data, which have been computed at the coupled cluster singles and doubles including connected triple excitations level and with the augmented correlation consistent polarized valence quintuple zeta basis set extended with a set of 3s3p2dlflg mid-bond functions [CCSD （T）/aug-cc-pV5Z-33211]. The close coupling calculation of state-to-state partial cross sections for collision of Ne with HC1 is first performed by employing the fitted interaction potential. This calculation is performed at the incident energies： 40, 60, 75 and 100 meV, separately. The effects of the long-range attractive and the short-range anisotropic interactions on the inelastic state-to-state partial cross sections are discussed in detail. Two maxima are present in the rotationally inelastic partial cross sections and they originate from different mechanisms.

Potential energy surfaces of ozone in the ground state

Equilibrium parameters of ozone, such as equilibrium geometry structure parameters, force constants and dissociation energy are presented by CBS-Q ab initio calculations. The calculated equilibrium geometry structure parameters and energy are in agreement with the corresponding experimental values. The potential energy function of ozone with a C2v symmetry in the ground state is described by the simplified Sorbie-Murrell many-body expansion potential function according to the ozone molecule symmetry. The contour of bond stretching vibration potential of an O3 in the ground state, with a bond angle （θ） fixed, and the contour of O3 potential for O rotating around O1-O （R1）, with O1-O bond length taken as the one at equilibrium, are plotted. Moreover, the potentials are analysed.

Quasi-Classical Trajectory Investigation of H+SO_(2)→OH+SO Reaction on Full-Dimensional Accurate Potential Energy Surface

The reaction H+SO_(2)→OH+SO is important in the combustion and atmospheric chemistry,as well as the interstellar medium.It also represents a typical complex-forming reaction with deep complexes,serving as an ideal candidate for testing various kinetics theories and providing interesting reaction dynamical phenomena.In this work,we reported a quasiclassical trajectory study of this reaction on our previously developed accurate full-dimensional potential energy surface.The experimental thermal rate coefficients over the temperature range 1400 K≤T≤2200 K were well reproduced.For the reactant SO_(2)being sampled at the ground ro-vibrational state,the calculated integral cross sections increased slightly along the collision energy ranging from 31.0 kcal/mol to 40.0 kcal/mol,and then became essentially flat at the collision energy within 40.0−55.0 kcal/mol.The product angular distributions are almost symmetric with nearly identical backward-forward double peak structure.The products OH and SO vibrational state distributions were also analyzed.

Full-Dimensional Potential Energy Surfaces of Ground(X^(2)A′)and Excited(A^(2)A″)Electronic States of HCO and Absorption Spectrum

In this work,high-fidelity full-dimensional potential energy surfaces(PESs)of the ground(X^(2)A′)and first doublet excited(A^(2)A″)electronic states of HCO were constructed using neural network method.In total,4624 high-level ab initio points have been used which were calculated at Davidson corrected internally contracted MRCI-F12 level of theory with a quite large basis set(ACV5Z)without any scaling scheme.Compared with the results obtained from the scaled PESs of Ndenguéet al.,the absorption spectrum based on our PESs has slightly larger intensity,and the peak positions are shifted to smaller energy for dozens of wavenumbers.It is indicated that the scaling of potential energy may make some unpredictable difference on the dynamical results.However,the resonance energies based on those scaled PESs are slightly closer to the current available experimental values than ours.Nevertheless,the unscaled high-level PESs developed in this work might provide a platform for further experimental and theoretical photodissociation and collisional dynamic studies for HCO system.

Globally accurate ab initio based potential energy surface of H_2O^+(X^4A'')

A globally accurate potential energy surface is reported for the electronic ground-state H2O＋. The ab initio energies utilized to map the potential energy surface are calculated at the multireference configuration interaction method employing the aug-cc-pVQZ basis set and the full valence complete active space wave function as reference. In order to improve accu- racy of the resulting raw ab initio energies, they are then extrapolated to the complete basis set limit and most importantly to the full configuration-interaction limit by semiempirically correcting the dynamical correlation using the double many- body expansion-scaled external correlation method. The topographical features of the current potential energy surface were examined in detail, which agree nicely with those of other theoretical work.

Accurate double many-body expansion potential energy surface of HS_2(A^2A') by scaling the external correlation

A globally accurate single-sheeted double many-body expansion potential energy surface is reported for the first excited state of HS_2 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 HS_2（A_2A＇） 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 HS_2（A_2A＇） 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.

A new global potential energy surface of the ground state of SiH_(2)^(+)(X^(2)A_(1))system and dynamics calculations of the Si^(+)+H_(2)(v_(0)=2,j_(0)=0)→SiH^(+)+H reaction

A global potential energy surface(PES)of the ground state of SiH_(2)^(+) system is built by using neural network method based on 18223 ab initio points.The topographic properties of PES are presented and compared with previous theoretical and experimental studies.The results indicate that the spectroscopic parameters obtained from the new PES are in good agreement with the experimental data.In order to further verify the validity of the new PES,a test dynamics calculation of the Si^(+)+H_(2)(v_(0)=2,j_(0)=0)→H+SiH^(+)reaction has been carried out by using the time-dependent wave packet method.The integral cross sections and rate constants are computed for the title reaction.The reasonable dynamical behavior indicates that the newly constructed PES is suitable for relevant dynamics investigations.

New ab initio Potential Energy Surfaces for Cl（^2P3/2,^2P1/2）＋H2 Reaction

New global three dimensional potential energy surfaces for the Cl＋H2 reactive system have been constructed using accurate multireference configuration interaction calculations with a large basis set. The three lowest adiabatic potential energy surfaces correlating asymptotically with Cl（^2p）＋H2 have been transformed to adiabatic representation, which leads to a fourth coupling potential for non-linear geometries. In addition, the spin-orbit coupling surfaces have also been computed using the Breit-Pauli Hamiltonian. Properties of the new potential are described. Reaction dynamics based on the new potential agrees with the recent experimental results quite well.

Theoretical Description of Water from Single-Molecule to Condensed Phase:Recent Progress on Potential Energy Surfaces and Molecular Dynamics

In this work,we review recent progress on the view of potential energy surfaces and molecular dynamics study of water and its related reactions in the last decade or so.Some important gas-phase reactions of water with radicals,chemisorbed dissociative dynamics of water on solid surfaces,and statistical mechanics and vibrational spectrum simulations of water from clusters to the condensed phase have been introduced.The recently developed machine learning techniques,such as the neural networks in a combination of permutational invariant polynomials or fundamental invariants,the atomic neural networks framework,the gaussian approximation potentials with the smooth overlap of atomic position kernel,as well as the many-body expansion framework for the construction of highly accurate potential energy surfaces,have also been discussed.Finally,some suggestions have been provided for further improvement of the potential energy surfaces and dynamics methods of water-related systems.