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Potential energy surface

About: Potential energy surface is a research topic. Over the lifetime, 11674 publications have been published within this topic receiving 307691 citations.


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Journal ArticleDOI
Abstract: Two different theoretical approaches are used to study the OH radical attack on toluene: the Moller−Plesset perturbation theory and the B3LYP density functional method. The critical points of the potential energy surface for the OH addition to toluene are determined, and rate−equilibrium relationships are discussed. A stable structure corresponding to a prereactive complex which is formed when the OH radical is at about 2.5 A from toluene is obtained. The existence of this loosely bound system is necessary to explain the experimentally observed negative activation energy. The geometry of transition states and products are determined for addition at different positions in the ring, including the ipso position, which has not been considered in previous works. Energy results at the MP4 and coupled cluster levels calculated at the optimized MP2 and B3LYP geometries confirm that the ipso adduct is more stable than the ortho adduct by about 0.5 kcal/mol. Several routes are proposed for the subsequent reactions...

70 citations

Journal ArticleDOI
TL;DR: In this article, a two-dimensional cut (C2v symmetry constraint) through the three-dimensional nuclear coordinate space, and specifically C-O bond lengths between 1.1 and 1.6 A and bending angles between 180 and 125° are examined.
Abstract: Electron attachment to CO2 is studied by exploring the parts of the potential energy surface where an electron can be bound in the fixed-nuclei picture. High level ab initio methods are used, and in particular the question of an adequate description of the threshold region, where the attachment energy goes to zero and the electronically bound anionic states become unstable, is discussed. Since the relevant coordinates are the symmetric stretching and the bending mode, we consider a two dimensional cut (C2v symmetry constraint) through the three dimensional nuclear coordinate space, and specifically C–O bond lengths between 1.1 and 1.6 A and bending angles between 180 and 125° are examined. Three bound CO2− states are identified in this region. The minimum associated with the long-lived CO2− state is localised on the lowest surface of the anion, and only a small barrier separates it from the region where the anion becomes unstable. Using earlier results from R-matrix calculations and our findings we can then answer the question which of the short-lived scattering states connects to the long-lived CO2− species. All three states of the CO2− anion are vibronically coupled, and the implications for the nuclear dynamics of these states are discussed, in particular in view of the recently observed vibrational excitation spectra.

70 citations

Journal ArticleDOI
TL;DR: In this article, the hyperquantization algorithm is applied to the prototypical exchange reaction F+H2→HF+H applying an exact quantum mechanical method, which exploits discrete analogs of hyperspherical harmonics and whose accuracy is tested for both differential and integral cross sections.
Abstract: We present in this article a numerical investigation of the dynamics of the prototypical exchange reaction F+H2→HF+H applying an exact quantum mechanical method, the hyperquantization algorithm, which exploits discrete analogs of hyperspherical harmonics and whose accuracy is tested for both differential and integral cross sections. The calculations employ the potential energy surface by Stark and Werner, both in its original version (SW PES) and in two new versions, properly adapted to include the effects of the long-range interaction in the reactants' valley (SW-LR) and also those due to the spin–orbit interaction (SW-LR-SO). The features of the potential surfaces in the entrance channel have been modeled according to experimental information coming from total cross section measurements carried out in our laboratory. Computed integral and differential cross sections for H2 in its ground vibrational state and for rotational states equal to 0, 1, 2 and 3 in the collision energy range 1.8–3.4 kcal mol−1 are compared with previous results by other accurate quantum mechanical methods (J. F. Castillo, B. Hartke, H.-J. Werner, F. J. Aoiz, L. Banares and B. Martinez-Haya, J. Chem. Phys., 1998, 109, 7224; M. H. Alexander, D. E. Manolopoulos and H.-J. Werner, J. Chem. Phys., 2000, 113, 11084) and with several sets of experimental data (differential cross sections (D. M. Neumark, A. M. Wodkke, G. N. Robinson, C. C. Hayden and Y. T. Lee, J. Chem. Phys., 1985, 82, 3045), nascent rovibrational distributions (W. B. Chapman, B. W. Blackmon, S. Nizkorodov and D. J. Nesbitt, J. Chem. Phys., 1998, 109, 9306.) and total integral cross sections (F. Dong, S.-H. Lee and K. Liu, J. Chem. Phys., 2000, 113, 3633.)) to emphasize the role of intermediate and long-range forces on reaction dynamics. The effect of the modifications of the ground surface due to spin–orbit interaction is also discussed and perspectives for future improvements are pointed out, the main indication being that the effective reaction barrier appears to be lower with respect to that of the original SW PES.

70 citations

Journal ArticleDOI
TL;DR: In this paper, the ICVT/MCPSAG theory and LSTH surface were employed to predict the rate coefficients for all three reactions in three dimensions. But they were not tested for sensitivity to variations in the potential energy surface by repeating the calculations for the less accurate Porter-Karplus surface.
Abstract: We consider three reactions: H+H2→H2+H; Mu+H2→MuH+H; Mu+D2 →MuD+D. We calculate accurate quantum mechanical reaction probabilities and thermal rate coefficients for all three reactions in collinear geometry using the Liu–Siegbahn–Truhlar–Horowitz (LSTH) accurate potential energy surface. These rate coefficients are used to test conventional transition state theory and the improved canonical variational theory with Marcus–Coltrin‐path semiclassical adiabatic ground‐state transmission coefficients (ICVT/MCPSAG). The ICVT/MCPSAG theory is found to be greatly superior and reasonably reliable. These conclusions are tested for sensitivity to variations in the potential energy surface by repeating the calculations for the less accurate Porter–Karplus surface. The conclusions are unaltered by this. The ICVT/MCPSAG theory and LSTH surface are then employed to predict the rate coefficients for all three reactions in three dimensions.

70 citations

Book ChapterDOI
TL;DR: A semiclassical model of the deuterium kinetic isotope effects has been proposed in this article, where the de Broglie wavelengths of hydrogen isotopes have been used to describe hydrogen transfer reactions.
Abstract: Publisher Summary An essential part of the understanding of enzyme catalysis is an experimental description of the mechanism, transition state structure, and potential energy surface of the reaction. A semiclassical picture of the reaction can be described from primary and secondary deuterium kinetic isotope effects. However, the isotopes of hydrogen [protium (H), deuterium (D), and tritium (T)] have de Broglie wavelengths that are similar to the distances they must typically travel during a hydrogen transfer reaction. This property has led to the recognition that the behavior of hydrogen is poised between classical and quantum mechanical realms. To describe the enzyme-catalyzed hydrogen transfers rigorously, these reactions need to be examined for quantum effects. Hydrogen tunneling has been shown to be a general feature of a variety of enzyme systems that have been examined. Some features of a chemical reaction that affect the tunneling probability and have been observed to be altered in enzyme-catalyzed reactions are the degree of participation of solvent reorganization, the thermodynamic relationship between substrates and products, and the height and width of the reaction coordinate energy barrier. The optimization of enzyme catalysis may entail the evolutionary implementation of these chemical strategies that increase the probability of tunneling, and thereby accelerate the reaction rate. Additionally, the exploration of variations in the extent of hydrogen tunneling offers a powerful new approach in determining how protein structure is linked to the optimization of enzyme catalysis.

70 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2023128
2022206
2021288
2020322
2019295
2018310