Potential energy surface PESs

Figures 3-4 and 3-5 show the optimized paths with the added images and the original combined method [27] and parallel path optimizer method [25] calculated paths for the first and second steps of the reaction respectively. In both cases, the addition of extra images on the converged path, and subsequent optimization of these extra images produces a smoother path since the additional images allows for a better mapping of the potential energy surfaces (PESs).

The F + H2 — HF + FI reaction is one of the most studied chemical reactions in science, and interest in this reaction dates back to the discovery of the chemical laser.79 In the early 1970s, a collinear quantum scattering treatment of the reaction predicted the existence of isolated resonances.80 Subsequent theoretical investigations, using various dynamical approximations on several different potential energy surfaces (PESs), essentially all confirmed this prediction. The term resonance in this context refers to a transient metastable species produced as the reaction occurs. Transient intermediates are well known in many kinds of atomic and molecular processes, as well as in nuclear and particle physics.81 What makes reactive resonances unique is that they are not necessarily associated with trapping... 

Free radicals are short-lived, highly-reactive transient species that have one or more unpaired electrons. Free radicals are common in a wide range of reactive chemical environments, such as combustion, plasmas, atmosphere, and interstellar environment, and they play important roles in these chemistries. For example, complex atmospheric and combustion chemistries are composed of, and governed by, many elementary processes involving free radicals. Studies of these elementary processes are pivotal to assessing reaction mechanisms in atmospheric and combustion chemistry, and to probing potential energy surfaces (PESs) and chemical reactivity. 

Recent years have witnessed a considerable activity towards extending the standard single-reference coupled-cluster (CC) methods (1-9) to potential energy surfaces (PESs) involving bond breaking without invoking a multireference description (see, e.g., refs 9-31). Undoubtedly, it would be very useful if we could routinely calculate large portions of molecular PESs with the ease-... 

Figure 2.1 Schematic representation of the ground and electronic excited potential energy surfaces (PESs) and the corresponding absorption spectra of the parent molecule, resulting from the reflection of different initial wavefunctions on a directly dissociative PES (a) absorption from a vibrationless ground state consists of a broad continuum and (b) absorption from a vibrationally excited state shows that extended regions are accessed, leading to a structured spectrum with intensities of the features being dependent on the Franck-Condon factors. Reproduced with permission from Ref. [34]. Reproduced by permission of lOP Publishing.

Analysis of the potential energy surfaces (PESs) of the interacting magnesium atoms and clusters shows that all processes of magnesium association are activationless. Then, the proportion between clusters of different composition would seem to be determined only by the lifetime of particles in the mobile layer and by the deposition rate from the gas phase. At first glance, there are no reasons for the predominant accumulation of more stable particles. The situation is different if the entropy factor is taken into account. 

Figure 20-6. B3LYP/6-31G calculated adiabatic and vertical potential energy surfaces (PESs) of ( ...

Figure 20-7. B3LYP/6-31++G" calculated adiabatic and vertical potential energy surfaces (PESs) of C5 -05/ bond dissociation of 5 -dTMPH radical anion. Energies and distances are given in kcal/mol and angstroms (A), respectively. The singly occupied molecular orbital (SOMO) is also shown. (Reprinted with permission from ref. [209], J. Phys. Chem. (2007) American Chemical Society.)...

The purpose of this chapter is to review some properties of isomerizing (ABC BCA) and dissociating (ABC AB + C) prototype triatomic molecules, which are revealed by the analysis of their dynamics on precise ab initio potential energy surfaces (PESs). The systems investigated will be considered from all possible viewpoints—quanmm, classical, and semiclassical mechanics—and several techniques will be applied to extract information from the PES, such as Canonical Perturbation Theory, adiabatic separation of motions, and Periodic Orbit Theory. 

The development of theory for reliable calculations of chemical dynamics has two components the construction of accurate, ab initio, multidimensional potential energy surfaces (PESs) and the performance of reactive scattering calculations, either by time-independent (TI) or time-dependent (TD) methods, on these surfaces. Accurate TI quantum methods for describing atom-diatom reactions, in particular for the benchmark H + H2 reaction, have been achieved since 1975.[1,2,3] Many exact and approximate theories have been tested with the H + H2 reaction.[4,5]... 

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