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The interaction between water and graphene is important for understanding the thermodynamic and kinetic properties of water on hydrophobic surfaces. In this study, we constructed a high-dimensional potential energy surface (PES) for the water-graphene system using the many-body expansion scheme and neural network fitting. By analyzing the landscape of the PES, we found that the water molecule exhibits a weak physisorption behavior with a binding energy of about − 1000 cm−1 and a very low diffusion barrier. Furthermore, extensive molecular dynamics were performed to investigate the adsorption and diffusion dynamics of a single water on a graphene surface at temperatures ranging from 50 to 300 K. Potential-of-mean-forces were computed from the trajectories, providing a comprehensive and accurate description of the water-graphene interaction kinetics.

Chemical reactions between Be+ ions and H2 molecules have significance in the fields of ultracold chemistry and astrophysics, but the corresponding dynamics studies on the ground-state reaction have not been reported because of the lack of a global potential energy surface (PES). Herein, a globally accurate ground-state BeH2+ PES is constructed using the neural network model based on 18,657 ab initio points calculated by the multi-reference configuration interaction method with the aug-cc-PVQZ basis set. On the newly constructed PES, the state-to-state quantum dynamics calculations of the Be+(2S) + H2(v0 = 0; j0 = 0) and Be+(2S) + D2(v0 = 0; j0 = 0) reactions are performed using the time-dependent wave packet method. The calculated results suggest that the two reactions are dominated by the complex-forming mechanism and the direct abstraction process at relatively low and high collision energies, respectively, and the isotope substitution has little effect on the reaction dynamics characteristics. The new PES can be used to further study the reaction dynamics of the BeH2+ system, such as the effects of rovibrational excitations and alignment of reactant molecules, and the present dynamics data could provide an important reference for further experimental studies at a finer level.

Artificial neural networks (ANN) have been shown for the last several years to be a versatile tool for fitting ab initio potential energy surfaces. We have demonstrated recently how a 60-neuron ANN could successfully fit a four-dimensional ab initio potential energy surface for the rigid rotor HeH+ - rigid rotor H2 system with a root-mean-squared deviation (RMSD) of 35 cm−1. We show in the present study how a (40, 40) neural network with two hidden layers could achieve a better fit with an RMSD of 5 cm−1. Through a follow-up quantum dynamical study of HeH+(j1)-H2(j2) collisions, it is shown that the two fits lead to slightly different rotational excitation and de-excitation cross sections but are comparable to each other in terms of magnitude and dependence on the relative translational energy of the collision partners. When averaged over relative translational energy, the two sets of results lead to rate coefficients that are nearly indistinguishable at higher temperatures thus demonstrating the reliability of the ANN method for fitting ab initio potential energy surfaces. On the other hand, we also find that the de-excitation rate coefficients obtained using the two different ANN fits differ significantly from each other at low temperatures. The consequences of these findings are discussed in our conclusions.

The interaction between CO2 and N2, both as essential components of the Earth’s atmosphere, plays a crucial role in investigating the greenhouse effect. In this work, we sampled 40,930 data points within the full-dimensional configuration space of CO2 and N2 and performed calculations at the level of explicitly correlated coupled cluster single, double, and perturbative triple level with the augmented correlation corrected valence triple-ζ basis set (CCSD(T)-F12a/AVTZ). To ensure computational accuracy while reducing computational costs, we employed the recently proposed Δ-machine learning (Δ-ML) method based on Permutation Invariant Polynomial-Neural Network (PIP-NN) for basis set superposition error (BSSE) correction. By leveraging the limited extrapolation capability of NN, efficient sampling was performed within the existing dataset, enabling the construction of the potential energy surface (PES) incorporating BSSE correction with only a small number of data points for BSSE calculations. A total of approximately 1100 data points were selected from the initial dataset to construct a BSSE correction PES. Utilizing this correction PES, BSSE predictions were carried out for all remaining data points, resulting in the successful development of a high-precision full-dimensional PES with BSSE correction for the CO2 + N2 system. The PIP-NN based Δ-ML method significantly reduced the required BSSE calculations by approximately 97.2%, resulting in a final PES with a fitting error of merely 0.026 kcal/mol.

An accurate interatomic potential energy surface for ground state of SH2− is reported at the multireference configuration interaction level of theory using aug–cc–pVQZ basis set. The calculated ab initio energy points are utilized, after semi-empirically correcting the dynamical correlation by the many-body expansion-scaled external correlation method. To verify the accuracy of the potential energy surface, molecular reaction dynamics, including the relationship between reaction probability and collision energy, thermal rate constant, and integral scattering cross section are calculated by using the quantum time-dependent wave packet method. The final results show that our potential energy surface is accurate and the molecular reaction dynamics results are satisfactory, and the accurate potential energy surface and its dynamics results can also lay a foundation for the future experimental research of SH−-containing molecules. This study provides a reasonable ionic chemical dissociation channel for the dynamics, A global many-body expansion (MEB) PES is reported by fitting high-precision ab initio energies calculated at the multireference configuration interaction level with Davidson correction (MRCI(Q)) and the aug-cc-pVQZ basis set (AVQZ). By comparing with the integral cross section with experimental result, which have agreement with the previous experimental and theoretical values. Our theoretical results can provide effective support for future dynamic experiments. [ABSTRACT FROM AUTHOR]

Potential energy surface was calculated for the ground electronic state of the triatomic ion ClO2− using the coupled-cluster method CCSD(T). Calculations were carried out for 1200 points on the potential energy surface, and the calculated points were fitted to the potential energy expression in terms of the internal coordinates, from which the quadratic, cubic and quartic force fields were determined. Using the second-order rovibrational perturbation theory, harmonic vibrational frequencies, anharmonicity constants and several other spectroscopic parameters were calculated, and accurate fundamental vibrational frequencies were obtained. Also, the energies of 30 lowest vibrational levels were calculated using the anharmonicity constants.

Chemical reactions between Be+ ions and H2 molecules have significance in the fields of ultracold chemistry and astrophysics, but the corresponding dynamics studies on the ground-state reaction have not been reported because of the lack of a global potential energy surface (PES). Herein, a globally accurate ground-state BeH2+ PES is constructed using the neural network model based on 18,657 ab initio points calculated by the multi-reference configuration interaction method with the aug-cc-PVQZ basis set. On the newly constructed PES, the state-to-state quantum dynamics calculations of the Be+(2S) + H2(v0 = 0; j0 = 0) and Be+(2S) + D2(v0 = 0; j0 = 0) reactions are performed using the time-dependent wave packet method. The calculated results suggest that the two reactions are dominated by the complex-forming mechanism and the direct abstraction process at relatively low and high collision energies, respectively, and the isotope substitution has little effect on the reaction dynamics characteristics. The new PES can be used to further study the reaction dynamics of the BeH2+ system, such as the effects of rovibrational excitations and alignment of reactant molecules, and the present dynamics data could provide an important reference for further experimental studies at a finer level. [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]

The reactive collision between Be atom and H2 molecule has received great interest both experimentally and theoretically due to its significant role in hydrogen storage, astrophysics, quantum chemistry and other fields, but the corresponding dynamics calculations have not been reported. Herein, a globally accurate ground-state BeH2 PES is represented using the neural network strategy based on 12371 high-level ab initio points. On this newly constructed PES, the quantum time-dependent wave packet calculations on the Be(1S) + H2(v0 = 0, j0 = 0) → BeH + H reaction are performed to study the microscopic dynamics mechanisms. The calculated results indicate that this reaction follows the complex-forming mechanism near the reactive threshold, whereas a direct H-abstraction process gradually plays the dominant role when the collision energy is large enough. The newly constructed PES can be used for further dynamics calculations on the BeH2 reactive system, such as the rovibrational excitations and isotopic substitutions of the H2 molecule, and the presented dynamics data would be of importance in experimental research at a finer level.

In this second paper, the individual-machine potential energy surface is established. The constant- $\theta _{i}$ angle surface of the machine is found in the angle space. Because the individual-machine potential energy is strictly zero in this angle surface, the constant- $\theta _{i}$ angle surface has a significant effect on the shape of the individual-machine potential energy surface. That is, the individual-machine potential energy surface is separated by a flat land, and mountains and valleys are located on either side of this flat land. In addition, a zero- $f_{i}$ angle surface also exists in the individual-machine potential energy surface. The individual-machine potential energy reaches a minimum or maximum at the surface. Using a scissor angle surface, the individual machine potential energy boundary that reflects the maximum individual-machine potential energy is obtained through the cut of the zero- $f_{i}$ angle surface. The machine becomes unstable after the system trajectory goes through the individual machine potential energy boundary. In the end, key concepts and distinctive phenomena in the individual-machine studies are fully explained using the concept of individual-machine potential energy surface.

The LiNa2 reactive system has recently received great attention in the experimental study of ultracold chemical reactions, but the corresponding theoretical calculations have not been carried out. Here, we report the first globally accurate ground-state LiNa2 potential energy surface (PES) using a Gaussian process model based on only 1776 actively selected high-level ab initio training points. The constructed PES had high precision and strong generalization capability. On the new PES, the quantum dynamics calculations on the Li(2S) + Na2(v = 0, j = 0) → LiNa + Na reaction were carried out in the 0.001–0.01 eV collision energy range using an improved time-dependent wave packet method. The calculated results indicate that this reaction is dominated by a complex-forming mechanism at low collision energies. The presented dynamics data provide guidance for experimental research, and the newly constructed PES could be further used for ultracold reaction dynamics calculations on this reactive system.

The status of machine learning in chemistry and related disciplines is becoming increasingly prominent, but its application in undergraduate chemistry experiments has yet to be seen. Existing computational chemistry experiments mostly focus on the application of quantum chemistry methods to study molecular properties and chemical reactions. In order to popularize machine learning as a powerful tool, this article will introduce a comprehensive computational chemistry experiment suitable for senior undergraduate students or graduate students. Through this experiment, students can gain a preliminary understanding of the basic principles and operational procedures of machine learning, while also develop their ability to apply quantum chemistry and machine learning to solve chemical problems. [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]

A new global potential energy surface (PES) of the ground state of the HN2 system is built using the neural network method. The aug-cc-pVQZ basis set for the H atom, cc-pwCVQZ basis set for the N atom and multi-reference configuration interaction method are employed in the ab initio calculations. The topographic features of the PES are discussed and compared with available theoretical studies. In addition, the initial state (v0 = 0, j0 = 0) dynamic studies of the N + NH(³Σ -) → N2(X¹ Σg +)+H reaction are performed using a time-dependent wave packet method, based on the newly constructed PES. The dynamics properties, such as reaction probabilities, integral crosssections, differential cross-sections, the rovibrational state distribution of product and rate constants, are calculated at the state-to-state level of theory and compared with available theoretical and experimental results. The differential cross-section indicates that the forward abstraction mechanism dominates the reaction with the increase of collision energy. [ABSTRACT FROM AUTHOR]

TDDFT scan calculations were performed for s-carborane-anthracene derivatives (o-CB-X-Ant where X=-H, -CH3, -C2H5 and tert-butyl or -tBu) in order to understand the interplay between the steric effects, S1 potential energy surface (PES) and photophysical properties. The results show that all systems exhibit three local minima on the S1 PES, which correspond to the emissive LE and TICT state, along with the nonemissive CT state respectively. In the case of the unsubstituted system (o-CB-H-Ant), and -CH3 and -C2H5 substituted cases, S1 PES is predicted to be quite flat for certain conformations indicating that it is possible for these systems to reach the nonemissive CT state without a large energy penalty. In comparison, conformational pathways for the nonemissive CT state are predicted to be energetically unfavorable for o-CB-tBu-Ant as a result of both steric and electronic effects. These results provide a mechanism for the enhanced emission of s-CB-fluorophore molecules with bulky ligands. [ABSTRACT FROM AUTHOR]

Based on a combination of valence-bond and molecular mechanics functions which were fitted to high-level ab initio calculations, we constructed an analytical full-dimensional potential energy surface, named PES-2020, for the hydrogen abstraction title reaction for the first time. This surface is symmetrical with respect to the permutation of the three hydrogens in ammonia, it presents numerical gradients and it improves the description presented by previous theoretical studies. In order to analyze its quality and accuracy, stringent tests were performed, exhaustive kinetics and dynamics studies were carried out using quasi-classical trajectory calculations, and the results were compared with the available experimental evidence. Firstly, the properties (geometry, vibrational frequency and energy) of all stationary points were found to reasonably reproduce the ab initio information used as input; due to the complicated topology with deep wells in the entrance and exit channels and a “submerged” transition state, the description of the intermediate complexes was poorer, although it was adequate to reasonably simulate the kinetics and dynamics of the title reaction. Secondly, in the kinetics study, the rate constants simulated the experimental data in the wide temperature range of 25–700 K, improving the description presented by previous theoretical studies. In addition, while previous studies failed in the description of the kinetic isotope effects, our results reproduced the experimental information. Finally, in the dynamics study, we analyzed the role of the vibrational and rotational excitation of the CN(v,j) reactant and product angular scattering distribution. We found that vibrational excitation by one quantum slightly increased reactivity, thus reproducing the only experimental measurement, while rotational excitation strongly decreased reactivity. The scattering distribution presented a forward-backward shape, associated with the presence of deep wells along the reaction path. These last two findings await experimental confirmation.

A new global many-body expansion potential energy surface (PES) for the ground electronic state of HO2 is constructed. All ab initio energy points are employed using aug-cc-pV(Q + d)Z and aug-cc-pV(5 + d)Z basis sets at the multi-reference conformational interaction level and then extrapolated to the complete basis set limit. The topographic characteristics of the global PES for HO2 (X 2A″) are discussed in detail and compared with experimental results, showing good agreement. We subsequently consider the O(3P) + OH(2Π) → O2(3 Σ g − ) + H(2S) reaction using the time-dependent wave packet method and calculate dynamics behaviors, including the vibration–rotation distribution and reaction probabilities. The results indicate that the new PES is suitable for dynamics investigations of O(3P) + OH(2Π) → O2(3 Σ g − ) + H(2S) and can be used as a component for PESs to construct larger oxygen/hydrogen containing systems. [ABSTRACT FROM AUTHOR]

We present a full-dimensional potential energy surface for Ar–SO2 which involves three intramolecular Q 1 , Q 2 and Q 3 normal modes for the ν 1 symmetric stretching, ν 2 bending and ν 3 asymmetric stretching vibrations of SO2. The intermolecular potential was computed at the [CCSD(T)]-F12a level with aug-cc-pVTZ basis set plus the midpoint bond functions (3s3p2d1f1g). Three vibrationally averaged potentials of Ar–SO2 with SO2 in the ground state as well as the ν 1 and ν 3 excited states were generated by integrating three intramolecular coordinates. Each potential has a global minimum with the non-planar geometry and two saddle points. The radial discrete variable representation (DVR)/angular finite basis representation (FBR) method and Lanczos algorithm were utilized to calculate the rovibrational bound states and energy levels of Ar–SO2. The vibrational band origin shifts for this complex in the ν 1 and ν 3 regions of SO2 were determined to be − 0.0970 and − 0.7537 cm−1, respectively. The calculated origin shifts as well as the microwave and infrared transition frequencies agree well with available experimental results. [ABSTRACT FROM AUTHOR]

The LiNa2 reactive system has recently received great attention in the experimental study of ultracold chemical reactions, but the corresponding theoretical calculations have not been carried out. Here, we report the first globally accurate ground-state LiNa2 potential energy surface (PES) using a Gaussian process model based on only 1776 actively selected high-level ab initio training points. The constructed PES had high precision and strong generalization capability. On the new PES, the quantum dynamics calculations on the Li(2S) + Na2(v = 0, j = 0) → LiNa + Na reaction were carried out in the 0.001–0.01 eV collision energy range using an improved time-dependent wave packet method. The calculated results indicate that this reaction is dominated by a complex-forming mechanism at low collision energies. The presented dynamics data provide guidance for experimental research, and the newly constructed PES could be further used for ultracold reaction dynamics calculations on this reactive system. [ABSTRACT FROM AUTHOR]

Based on 17,326 ab initio points, a global potential energy surface (PES) of the ground state of the CsH2 system was constructed using the neural network method. In ab initio calculations, the AVQZ basis set was used for the H atom, the def2-QZVP basis set was adopted for the Cs atom, and a multi-reference configuration interaction method was employed. The topographical characteristics of the newly developed PES were discussed in detail and no wells or barriers were detected. In addition, the dynamical calculations of the H + CsH reaction were performed using the time-dependent wave packet method, based on the new PES. Dynamics properties, such as reaction probability, integral cross section and differential cross-section were examined. The differential cross-section results indicated that the forward abstraction mechanism dominated the abstraction channel, and the 'rebound' reaction mechanism played a primary role in the exchange channel. Highlights Using the PIP-NN method, A global potential energy surface for the ground state of the CsH2 system was built based on 17,326 ab initio points. Dynamic calculations for the abstraction and exchange channels of the H + CsH reaction were performed using the time-dependent wave packet method and the dynamic properties of these two channels were discussed in detail. The direct abstraction mechanism plays a dominant role in the abstraction channel and the 'rebound' mechanism dominates the exchange channel. [ABSTRACT FROM AUTHOR]