Analytical potential energy surface

The multiple spawning method described in Section IV.C has been applied to a number of photochemical systems using analytic potential energy surfaces. As well as small scattering systems [36,218], the large retinal molecule has been treated [243,244]. It has also been applied as a direct dynamics method. 

Ah initio trajectory calculations have now been performed. However, these calculations require such an enormous amount of computer time that they have only been done on the simplest systems. At the present time, these calculations are too expensive to be used for computing rate constants, which require many trajectories to be computed. Semiempirical methods have been designed specifically for dynamics calculations, which have given insight into vibrational motion, but they have not been the methods of choice for computing rate constants since they are generally inferior to analytic potential energy surfaces fitted from ah initio results. 

POLYRATE can be used for computing reaction rates from either the output of electronic structure calculations or using an analytic potential energy surface. If an analytic potential energy surface is used, the user must create subroutines to evaluate the potential energy and its derivatives then relink the program. POLYRATE can be used for unimolecular gas-phase reactions, bimolecular gas-phase reactions, or the reaction of a gas-phase molecule or adsorbed molecule on a solid surface. 

The analytic potential energy surfaces, used for the Cl + CH3Clb and Cl + CHjBr trajectory studies described here, should be viewed as initial models. Future classical and quantum dynamical calculations of SN2 nucleophilic substitution should be performed on quantitative potential energy functions, derived from high-level ab initio calculations. By necessity, the quantum dynamical calculations will require reduced dimensionality models. However, by comparing the results of these reduced dimensionality classical and quantum dynamical calculations, the accuracy of the classical dynamics can be appraised. It will also be important to compare the classical and quantum reduced dimensionality and classical complete dimensionality dynamical calculations with experiment. 

R. Sayos, J. Hernando, J. Flijazo, M. Gonzalez, An analytical potential energy surface of the HFCL(2A ) system based on ab initio calculations. Variational transition state theory study of the H+C1F F+HC1,C1+HF, and F+HCl Cl+HF reactions and their isotope variants, Phys. Chem. Chem. Phys. 1 (1999) 947. 

Murrel and co-workers [39] have developed a functional form in which the global analytic potential energy surface is written as a sum of N-body terms... 

Hrovat, D. A. Fang, S. Borden, W. T. Carpenter, B. K. Investigation of cyclopropane stereomutation by quasiclassical trajectories on an analytical potential energy surface, ... 

This simple model and also the produced analytical potential energy surface (PES) will be used to explore the structure, the geometry, and the stability of Li2" -XCn clusters. 

Gilibert, M., Aguilar, A., Gonzales, M., Mota, R Sayos, R. (1992). Dynamics of the N Su) + NO(X n) —> N2 (X E+) + OifPg) atmospheric reaction on the A" ground potential energy surface. 1. Analytical potential energy surface and preliminary quasiclassical trajectory calculation, /. Chem. Phys. 97 5542-5552. 

The efforts on the construction of the potential energy have successfully produced several versions of an analytical potential energy surface that can be used in dynamical studies—to name a few, the recent potential energy surface of Bowman and co-workers, and the recent PES-2006 of Espinosa-Garcia et In our quantum dynamical study and rate constant computation, we employed the PES-2006 version. The ZPE-corrected PES of this version has a negative barrier of —0.07 kcal mol with respect to the ZPE-corrected reactants. ... 

Chemical dynamics simulations were performed to study the unimolecular decomposition of microcanonical ensembles versus energy of the Cl — CH Br ion lipole complex.An analytic potential energy surface was used for the simulations. The complex has two unimolecular reaction paths, i.e. dissociation to C/ + CHjBr or isomerization to the CICH —Br ion iipole complex. The simulations were performed for energies of 30-80 kcal mol and the resulting non-exponential N t)IN 0) were lit by a sum of three exponentials, i.e. eqn (20.18). The resulting// and ki fitting parameters are listed in Table 20.2. 

Fourth-order Runge-Kutta and various predictor-corrector methods have been used successfully for reaction path following, especially on analytical potential energy surfaces. Page and Mclver have extended the LQA and CLQA methods... 

Traditional Approach Analytic Potential Energy Surfaces... 

Investigation of Cyclopropane Stereomutation by Quasiclassical Trajectories on an Analytical Potential Energy Surface. 

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