Features Of Potential Energy Surface Research Articles

Minimizing Redundancy and Data Requirements of Machine Learning Potential: A Case Study in Interface Combustion.

The machine learning potential has emerged as a promising approach for addressing the accuracy-versus-efficiency dilemma in molecular modeling. Efficiently exploring chemical spaces with high accuracy presents a significant challenge, particularly for the interface reaction system. This study introduces a workflow aimed at achieving this goal by incorporating the classical SOAP descriptor and practical PCA strategy to minimize redundancy and data requirements, while successfully capturing the features of complex potential energy surfaces. Specifically, the study focuses on interface combustion behaviors within promising alloy-based solid propellants. A neural network potential model tailored for modeling AlLi-AP interface reactions under varying conditions is constructed, showcasing excellent predictive capabilities in energy prediction, force estimation, and bond energies. A series of large-scale MD simulations reveal that Li doping significantly influences the initial combustion stage, enhancing reactivity and reducing thermal conductivity. Mass transfer analysis also highlights the considerably higher diffusion coefficient of Li compared to Al, with the former being three times greater. Consequently, the overall combustion process is accelerated by approximately 10%. These breakthroughs pave the way for virtual screening and the rational design of advanced propellant formulations and microstructures incorporating alloy-formula propellants.

A New Ab Initio Potential Energy Surface and Rovibrational Spectra for the CO-N2O Complex.

We constructed a new ab initio potential energy surface (PES) for CO-N2O which includes the intramolecular Q3 normal coordinate for the N2O ν3 antisymmetric stretching vibration. The intermolecular potential was evaluated employing the supermolecular method at the [CCSD(T)]-F12a level, with the aug-cc-pVTZ basis set plus bond functions. By integral over the intramolecular Q3 coordinate, we obtained the vibrationally averaged PESs for the CO-N2O system in the ground and ν3 excited states of N2O. Each PES features one nearly T-shaped global minimum and one skewed T-shaped local minimum. Based on these obtained PESs of CO-N2O, the radial discrete variable representation/angle finite base representation method and the Lanczos algorithm were applied for the calculations of bound states and rovibrational energy levels. The calculated ν3 vibrational band origin shift of the N2O monomer in CO-N2O is 2.7570 cm-1, matching well with the observed value of 2.9048 cm-1. The computed microwave and infrared transition frequencies, as well as the rotational parameters, are consistent with the experimental observations.

"On-the-fly" : How to reliably and automatically characterize and construct potential energy surfaces.

In this work, the code, developed previously by the authors to find "holes" as well as legitimate transition states in existing potential energy surface (PES) functions [JPC Lett. 11, 6468 (2020)], is retooled to perform on-the-fly "direct dynamics"-type PES explorations, as well as automatic construction of new PES functions. In all of these contexts, the chief advantage of over other methods is its ability to globally map the PES, thereby determining the most relevant regions of configuration space quickly and reliably-even when the dimensionality is rather large. Here, is used to generate a uniformly spaced grid of density functional theory (DFT) or ab initio points, truncated over the relevant regions, which can then be used to either: (a) hone in precisely on PES features such as minima and transition states, or; (b) create a new PES function automatically, via interpolation. Proof of concept is demonstrated via application to three molecular systems: water (H O), (reduced-dimensional) methane (CH ), and methylene imine (CH NH).

Regular reaction dynamics in analytical form in the vicinity of symmetrical transition states. Central barrier crossings in SN2 reactions.

When an activated complex, as defined in transition state theory (TST), has a polyhedral shape, its kinetic energy is found to be diagonal in a system of spherical polar coordinates. If, in addition, the polyhedron is characterized by a high symmetry, then its dynamics considerably simplifies. An application of this approach to the most symmetrical TS known to date, i.e., that which controls the Cl- + CH3Cl → ClCH3 + Cl- SN2 nucleophilic substitution, is presented and an analytical expression of its potential energy surface is provided. In a substantial range around the saddle point, approximate equations of motion for the two components of the reaction coordinate, i.e., the antisymmetrical stretching motion of the ClCCl core and the wagging motion of the hydrogen triad, can be derived in an analytical form. During an extensive period of time, the main component of the reaction coordinate is governed by an unexpectedly simple equation of motion that depends on a single initial condition, irrespective of the other ones and of the internal energy. Reactive trajectories are observed to form a perfectly collimated bundle characterized by undetectable dispersion, thereby giving a spectacular example of regular dynamics in an anharmonic potential. Regularity and collimation are brought about by local symmetry, which is a widespread feature of potential energy surfaces. Anharmonicity is observed to influence the dynamics only at a late stage. As energy increases, trajectories tend to fan out and to deviate from the analytical equation. For the wagging motion, chaos sets in at much lower energies.

Exploring Ligand-to-Metal Charge-Transfer States in the Photo-Ferrioxalate System Using Excited-State Specific Optimization.

The photo-ferrioxalate system (PFS), [Fe(III)(C2O4)]3-, more than an exact chemical actinometer, has been extensively applied in wastewater and environment treatment. Despite many experimental efforts to improve clarity, important aspects of the mechanism of ferrioxalate photolysis are still under debate. In this paper, we employ the recently developed WΓ-CASSCF to investigate the ligand-to-metal charge-transfer states that are key to ferrioxalate photolysis. This investigation provides a qualitative picture of these states and key potential energy surface features related to the photolysis. Our theoretical results are consistent with the prompt charge-transfer picture seen in recent experiments and clarify some features that are not visible in experiments. Two ligand-to-metal charge-transfer states contribute to the photolysis of ferrioxalate, and the avoided crossing barrier between them is low compared with the initial photoexcitation energy. Our data also clarify that one Fe-O bond cleaves first, followed by the C-C bond and the other Fe-O bond.

Rotational state-changes in C5N− by collisions with He and H2

ABSTRACT The anion C5N− is one of the largest linear (C,N)-bearing chains detected in the interstellar medium. Here we present and discuss the general features of new ab initio potential energy surfaces describing the interaction of this linear anion with He and H2. We employ a Legendre Polynomials expansion representation for the former and an artificial neural network fit for the latter. We then carry out quantum scattering calculations to yield rotationally inelastic cross-sections for collisions with He and H2, using relative translational energy values in the range of 0.1–300 cm−1. We then obtained the corresponding inelastic rate coefficients as a function of temperature covering the range from 1 to 100 K. The results for these two systems are compared with each other, as well as with the earlier results on the C3N− colliding with the same partners. We found that the final inelastic rate coefficients for this anion are all fairly large, those from collisions with H2 being the largest. The consequences of such findings on their non-equilibrium rotational populations in interstellar environments are discussed in our conclusions.

An accurate many-body expansion potential energy surface for AlH2 (22A') and quantum dynamics in Al(3P) + H2 (v0 = 0-3, j0 = 0, 2, 4, 6) collisions.

An accurate potential energy surface is constructed for the excited state of AlH2 by fitting extensive ab initio points calculated at the multi-reference configuration interaction level based on aug-cc-pV(Q+d)Z and aug-cc-pV(5+d)Z basis sets. All the calculated energies are corrected via the many-body expansion method and extrapolated to the complete basis set limit. The various topographic features of the new potential energy surface are investigated to demonstrate the correct behavior of Al(3P) + H2(X1Σg+) and AlH(a3Π) + H(2S) dissociation limits. By employing the time-dependent wave packet approach, the integral scattering cross-sections obtained from the Coriolis coupling calculation and the centrifugal sudden approximation, respectively, are compared in detail and show that the former has a higher effect on the reaction. Moreover, the thermal rate constants for Al(3P) + H2 (v0 = 0-3, j0 = 0, 2, 4, 6) in the temperature range of 0-5000 K are calculated, thereby providing insights into the influence of ro-vibrational quantum numbers on the thermal rate constants.

An accurate many-body expansion potential energy surface for SiH2 (11 A') using a switching function formalism.

An accurate many-body expansion potential energy surface for the ground state of SiH2 is reported. To warrant the correct behavior at the Si (1D) + H2 (X1Σ+g) dissociation channels involving silicon in the first excited Si (1D) and ground Si (3P) states, a switching function formalism has been utilized. A great deal of ab initio points based on aug-cc-pV(Q+d)Z and aug-cc-pV(5+d)Z basis sets are utilized at the multi-reference configuration interaction level using the full-valence-complete-active-space wave function as the reference. Subsequently the calculated energies are corrected via a many-body expansion method to extrapolate to the complete basis set limit. The topographic features of the novel many-body expansion global potential energy surface are studied in detail, showing a good agreement with the theoretical and experimental results in the literature. Moreover, the integral cross-section of the Si (1D) + H2 (X1Σ+g) → H (2S) + SiH (X2Π) reaction has been calculated using the time-dependent wave packet method, which provides support for the reliability of the title potential energy surface. This work can serve as the foundation for the study of Si (1D) + H2 (X1Σ+g) reaction kinetics, and for the construction of the larger multibody expansion potential energy surface of silicon/hydrogen containing systems.

Globally Accurate Potential Energy Surface for BH2+2(13A') Using the Switching Function Formalism.

A great number of ab initio energy points are calculated using the aug-cc-pV(Q,5)Z basis sets at the multireference configuration interaction level and extrapolated to the complete basis set limit. An exact three-dimensional potential energy surface of the ground-state BH2+ is obtained. A switching function is developed to model the transition of B+(3P) to B+(1S) to guarantee the reliable behavior at B+(3P) + H2(X1∑g+) and BH+(X2∑+) + H(2S) dissociation limits. The various topographic features of the new global potential energy surface are discussed in detail, showing a good agreement with the previous results from the theory. The quasi-classical trajectory method is utilized to calculate the integral cross sections of the B+(3P) + H2(X1∑g+) (v = 0, j = 0) → BH+(X2∑+) + H(2S) reaction, which can provide another support for reliability of the title potential energy surface.

A state-averaged orbital-optimized hybrid quantum–classical algorithm for a democratic description of ground and excited states

In the noisy intermediate-scale quantum (NISQ) era, solving the electronic structure problem from chemistry is considered as the ‘killer application’ for near-term quantum devices. In spite of the success of variational hybrid quantum/classical algorithms in providing accurate energy profiles for small molecules, careful considerations are still required for the description of complicated features of potential energy surfaces. Because the current quantum resources are very limited, it is common to focus on a restricted part of the Hilbert space (determined by the set of active orbitals). While physically motivated, this approximation can severely impact the description of these complicated features. A perfect example is that of conical intersections (i.e. a singular point of degeneracy between electronic states), which are of primary importance to understand many prominent reactions. Designing active spaces so that the improved accuracy from a quantum computer is not rendered useless is key to finding useful applications of these promising devices within the field of chemistry. To answer this issue, we introduce a NISQ-friendly method called ‘state-averaged orbital-optimized variational quantum eigensolver’ which combines two algorithms: (1) a state-averaged orbital-optimizer, and (2) a state-averaged VQE. To demonstrate the success of the method, we classically simulate it on a minimal Schiff base model (namely the formaldimine molecule CH2NH) relevant also for the photoisomerization in rhodopsin—a crucial step in the process of vision mediated by the presence of a conical intersection. We show that merging both algorithms fulfil the necessary condition to describe the molecule’s conical intersection, i.e. the ability to treat degenerate (or quasi-degenerate) states on the same footing.

Identification and Reactivity of s-cis,s-cis-Dihydroxycarbene, a New [CH2O2] Intermediate.

We report the first preparation of the s-cis,s-cis conformer of dihydroxycarbene (1cc) by means of pyrolysis of oxalic acid, isolation of the lower-energy s-trans,s-trans (1tt) and s-cis,s-trans (1ct) product conformers at cryogenic temperatures in a N2 matrix, and subsequent narrow-band near-infrared (NIR) laser excitation to give 1cc. Carbene 1cc converts quickly to 1ct via quantum-mechanical tunneling with an effective half-life of 22 min at 3 K. The potential energy surface features around 1 were pinpointed by convergent focal point analysis targeting the AE-CCSDT(Q)/CBS level of electronic structure theory. Computations of the tunneling kinetics confirm the time scale of the 1cc → 1ct rotamerization and suggest that direct 1cc → H2 + CO2 decomposition may also be a minor pathway. The intriguing latter possibility cannot be confirmed spectroscopically, but hints of it may be present in the measured kinetic profiles.

Probing the Potential Energy Surfaces of BrCN- by Dissociative Electron Attachment.

State coupling certainly determines the topologic features of the molecular potential energy surface (PES) and potentially diversifies chemical reaction pathways. Here we report the new PESs of BrCN- in the low-lying electronic states that are distinctly different from the previous predictions in the short Br-CN bond region but validated by the high-resolution ion velocity imaging measurements of low-energy dissociative electron attachment (DEA) to BrCN. Besides the vibrating CN- ions produced in the fast Br-CN bond stretching motions, we confirm that the ro-vibrating CN- ions with a nearly isotropic angular distribution are produced by receiving a torque in the combinational motion of Br-CN bond bending and stretching. The latter process is closely related to the potential well of BrCN- at the first excited state A2Π3/2 that arises from the Π-Σ state couplings. Our findings not only suggest that the PESs of other anionic cyanogen halides are in dire need of reexamination but also show that ion velocity imaging of the DEA process is a powerful experimental method for evaluating the theoretical PESs of molecular anions.

Improving Excited-State Potential Energy Surfaces via Optimal Orbital Shapes

We demonstrate that, rather than resorting to high-cost dynamic correlation methods, qualitative failures in excited-state potential energy surface predictions can often be remedied at no additional cost by ensuring that optimal molecular orbitals are used for each individual excited state. This approach also avoids the weighting choices required by state-averaging and dynamic weighting and obviates their need for expensive wave function response calculations when relaxing excited-state geometries. Although multistate approaches are of course preferred near conical intersections, other features of excited-state potential energy surfaces can benefit significantly from our single-state approach. In three different systems, including a double bond dissociation, a biologically relevant amino hydrogen dissociation, and an amino-to-ring intramolecular charge transfer, we show that state-specific orbitals offer qualitative improvements over the state-averaged status quo.

Combined experimental and theoretical study on the ultraviolet photodissociation dynamics of 1-bromo-2,6-difluorobenzene in 267 nm-234 nm.

Thanks to their specific molecular symmetry, aromatic molecules and their derivatives represent ideal model systems in understanding photo-induced chemistry of small molecules. Herein, ultraviolet photodissociation dynamics of the 1-bromo-2,6-difluorobenzene molecule has been visualized via imaging the recoiling velocity distributions of photofragments. The measured recoiling angular distributions of the Br(2P3/2) product vary significantly with the increasing photon energy, arguing against the simple bond-fission mechanism within the C2v symmetry. Ab initio calculations reveal that in addition to the C-Br bond cleavage, two additional internal molecular coordinates that break the molecular symmetry are likely involved. The Br out-of-plane bending opens a direct dissociation pathway on the S1-1A″ (S1-1ππ*) state, while the asymmetric C-F stretching significantly changes the orientation of the transition dipole moment. The present study sheds new light on the effect of symmetry breaking in the photodissociation dynamics of symmetric aryl halides, highlighting the multi-dimensional feature of excited state potential energy surfaces.

A Global Full-Dimensional Potential Energy Surface for the K2Rb2 Complex and Its Lifetime.

A full-dimensional global potential energy surface for the KRb + KRb → K2 + Rb2 reaction is developed from 20 759 ab initio points calculated using a coupled cluster singles, doubles, and perturbative triples (CCSD(T)) method with effective core potentials, extrapolated to the complete basis set limit. The ab initio points are represented with high fidelity (root-mean-square error of 1.86 cm-1) using the permutation-invariant polynomial-neural network method, which enforces the permutation invariance of the potential with respect to exchange of identical nuclei. The potential energy surface features two D2h minima and one Cs minimum connected by the isomerization saddle points. The Rice-Ramsperger-Kassel-Marcus lifetime of the K2Rb2 reaction intermediate estimated using the potential energy surface is 227 ns, in reasonable agreement with the latest experimental measurement.

A full-dimensional ab initio intermolecular potential energy surface and ro-vibrational spectra for N2-HF and N2-DF.

A full-dimensional ab initio intermolecular potential energy surface (IPES) is reported in this paper for van der Waals complex N2-HF. The calculations were performed by employing the explicitly correlated coupled cluster [CCSD (T)-F12a] method with the augmented correlation-consistent aug-cc-pVTZ basis set plus bond functions. The basis set superposition error was corrected by the full counterpoise procedure. About 55 000 ab initio points were calculated and then fitted by the permutation invariant polynomial neural network approach with a root-mean-square error of 0.433 cm-1. The potential energy surface features two equivalent linear minima with a well depth of 811.012 cm-1 separated by a barrier of 635.836 cm-1. The ro-vibrational energy levels for N2-HF and N2-DF were calculated based on the vibrationally averaged 4D IPESs with the radial discrete variable representation/angular finite basis representation method and Lanczos propagation algorithm. The calculated frequencies and the relative line intensities in the HF (DF) stretching band agree well with the available observed spectra. The theoretical band origins are all red shifted relative to the isolated HF (DF) molecule and reproduce the experimental values well. The results of ro-vibrational state calculations demonstrate the high accuracy of our new PES.

Spin-Forbidden Reactivity of Transition Metal Oxo Species: Exploring the Potential Energy Surfaces.

Spin-forbidden reactions are frequently encountered when transition metal oxo species are involved, particularly in oxygen transfer reactivity. The computational study of such reactions is challenging, because reactants and products are located on different spin potential energy surfaces (PESs). One possible approach to describe these reactions is the so-called minimum energy crossing point (MECP) between the diabatic reactants and products PESs. Alternatively, inclusion of spin-orbit coupling (SOC) effects allows to locate a saddle point on a single adiabatic PES (TS SOC). The TS SOC approach is rarely applied because of its high computational cost. Recently evidence for a TS SOC impact on significantly lowering the activation barrier in dioxygen addition to a carbene-gold(I)-hydride complex reaction (Chem. Sci. 2016, 7, 7034-7039) or even on predicting a qualitatively different reaction mechanism in mercury methylation by cobalt corrinoid (Angew. Chem. Int. Ed. 2016, 55, 11503-11506) has been put forward. Using MECP and TS SOC approaches a systematic analysis is provided here of three prototypical transition metal oxo spin-forbidden processes to investigate their implications on reactivity. Cycloaddition of ethylene to chromyl chloride (CrO2 Cl2 +C2 H4 ), iron oxide cation insertion into the hydrogen molecule (FeO+ +H2 ) and H-abstraction from toluene by a MnV -oxo-porphyrin cation (MnOP(H2 O)+ +C6 H5 CH3 ) are case studies. For all these processes the MECP and TS SOC results are compared, which show that the spin-forbidden reactivity of transition metal oxo species can be safely described by a MECP approach, at least for the first-row transition metals investigated here, where the spin-orbit coupling is relatively weak. However, for the Mn-oxo reactivity, the MECP and TS SOC have been found to be crucial for a correct description of the reaction mechanism. In particular, the TS SOC approach allows to straightforwardly explore detailed features of the adiabatic potential energy surface which in principle could affect the overall reaction rate in cases where the involved diabatic PESs are tricky.

Accurate global adiabatic potential energy surface for the ground state of AlH2+ by extrapolation to the complete basis set limit

ABSTRACT has very important research significance as the intermediate product of free radical . However, in Bell and Simons's [J. Phys. Chem. A. 103, 539–549 (1999)] study about , the maximum value of the integral cross section is about twice as large as the experimental value, which is caused by the lack of a precise global potential energy surface. An accurate full three-dimensional global potential energy surface for the electronic ground state of is reported in this paper by fitting a large amount of ab initio energies extrapolated to the complete basis set limit, which calculated based on aug-cc-pV(Q,5)Z basis sets and the multi-reference configuration interaction method with Davidson correction. The main geomorphic features of the novel potential energy surface are carefully investigated and have a great agreement with previous works. For examining the correctness of the new potential energy surface, based on the reaction , the integral cross section is calculated by employing the time-dependent wave packet theory and quasi-classical trajectory method. The dynamic results of two methods are in good agreement with the experimental values, which indicates the novel potential energy surface perfectly solves the divergence between the theoretical and the experimental value.

Accurate global potential energy surface by extrapolation to the complete basis set limit and dynamics studies for ground state of H2S.

The atomic ions with hydrogen reactions play important role in biological chemistry, atmospheric and combustion chemistry. In this work, a full three-dimensional global many-body expansion potential energy surface (PES) for the ground state of H2S-(2A') is reported for the first time, since there is almost no investigations can accurately and completely describe the PES. It is obtained using many-body expansion theory and an extensive set of accurate ab initio energies extrapolated to the complete basis set limit, for improving the accuracy of the potential energy surface. The topographical features of the new three-dimensional global potential energy surface are examined in detail, and found to be in good agreement with theoretical and experimental results. To better test the reaction, such a surface was applied to quasi classical trajectory calculations for S-(2P)+H2(1Σg+)→SH-(1Σ)+H(2S) reaction. The integral cross sections, differential cross sections and the rate coefficients have been computed. Results indicate that such a work can be recommended for corresponding atmospheric dynamics studies and as building blocks for constructing the many body expansion potential energy surface of larger S-/H containing systems.

Designing Reactions with Post-Transition-State Bifurcations: Asynchronous Nitrene Insertions into C–C σ Bonds

Summary Discoveries of chemical reactions with potential energy surfaces with post-transition-state bifurcations are increasing in frequency. Although such potential energy surface features are often discovered accidentally, we demonstrate here that they can be designed rationally. We describe a process for designing such reactions and apply it to the design of a nitrene addition/alkyl-shift reaction with a post-transition state bifurcation. We examine substituent effects on this reaction and propose a dynamics-based model for selectivity control.