London-Eyring-Polanyi-Sato

A multidimensional PES for the reaction (6.45a) has been calculated by Wight et al. [1993] with the aid of the atom-atom potential method combined with the semiempirical London-Eyring-Polanyi-Sato method (see, e.g., Eyring et al. [1983]). Because of high exoergicity, the PES... 

One formalism which has been extensively used with classical trajectory methods to study gas-phase reactions has been the London-Eyring-Polanyi-Sato (LEPS) method . This is a semiempirical technique for generating potential energy surfaces which incorporates two-body interactions into a valence bond scheme. The combination of interactions for diatomic molecules in this formalism results in a many-body potential which displays correct asymptotic behavior, and which contains barriers for reaction. For the case of a diatomic molecule reacting with a surface, the surface is treated as one body of a three-body reaction, and so the two-body terms are composed of two atom-surface interactions and a gas-phase atom-atom potential. The LEPS formalism then introduces adjustable potential energy barriers into molecule-surface reactions. 

This expression has seen many developments through the years and has evolved into the so-called London-Eyring-Polanyi-Sato (LEPS) surface in which expression (30) is multiplied by an empirical factor (1 + k)" which is supposed to take account of overlap effects (90). The coulomb and exchange integrals are calculated from the singlet and triplet potential curves of the diatomics, given by the expressions... 

The VB simplified model of ground-state potential energy surface H3 system considered as transition state and stabilization valleys of the H + H2 reaction is also an early problem, belonging to the history of physical chemistry under the name London-Eyring-Polanyi-Sato (LEPS) model that continues to serve as basis of further related developments [17,18], The actual analysis is a new a focus on the JT point of this potential energy surface able to absorb results of further renewed CASCCF type calculations on this important system. 

The London-Eyring-Polanyi-Sato (LEPS) method is a semi-empirical method.8 It is based on the London equation, but the calculated Coulombic and exchange integrals are replaced by experimental data. That is, some experimental input is used in the construction of the potential energy surface. The LEPS approach can, partly, be justified for H + H2 and other reactions involving three atoms, as long as the basic approximations behind the London equation are reasonable. 

For their calculations, Polanyi and co-workers and Karplus, Porter, and Sharma (20) have employed versions of the LEPS (London-Eyring-Polanyi-Sato) potential, which has some connection with formal theory since it is based on the London equation for a system of three atoms [320] ... 

LEPS (London-Eyring—Polanyi—Sato) Potential—approximate polyatomic potential surface obtained from diatomic Morse functions and related repulsive functions. 

It appears to be difficult to state general conditions as to when reactive trajectories in reactions of an atom with a polyatomic molecule could be expected to be reasonably straight lines up to the barrier. In the case of A + BC reactions, however, the problem in question was studied in considerable detail for O + HCl (DCl) reactions [45-48] on two London-Eyring-Polanyi-Sato (LEPS) potential surfaces [49] usually referred to as Surface 1 and Surface II. The two surfaces, although perhaps not very accurate, nevertheless allow us to draw important conclusions of quite general validity. They differ mainly in the shape of the equipotential contours in the region near the H atom ... 

In the London-Eyring-Polanyi-Sato (LEPS) method224 the original London equation is multiplied by an empirical factor which is supposed to account for the effect of overlap. 

Molecular dynamics studies of diatomic model detonations were first carried out by Karo and Hardy in 1977 [14]. They were soon followed by other groups [15, 16]. These early studies employed predissociative potentials, in which the reactant dimer molecules are metastable and can dissociate exothermically. More realistic models, combining an endothermic dissociation of reactants with an exothermic formation of product molecules, were introduced by White and colleagues at the Naval Research Laboratory and U.S. Naval Academy, first using a LEPS (London-Eyring-Polanyi-Sato) three-body potential for nitric oxide [17], and later a Tersoff-type bond-order potential [18] for a generic AB model, loosely based on NO [19, 20]. 

Another early attempt to incorporate chemieal reactions into molecular dynamics of shock waves was the use of the LEPS (London, Eyring, Polanyi, Sato) potential [4], originally developed in the 1930 s to model the H3 potential energy surface. This method can be applied to systems in which each atom interacts with exactly two nearest neighbors, and is therefore suitable for modeling one-dimensional reactive chains [5-6]. It provides a more realistic treatment of energy release as a function of bond formation but is not readily extended to more complex systems. 

Instead of performing the normal mode analysis we have used a more approximate method to take the qr- -coordinates into account. For the Cl - - CH4/CD4 reactions wc have in some work used a tanh-function in the breaking bond to interpolate between the saddle point and the product asymptote to get both the reaction thermicity and AfA" consistent with the ah initio calculations[18]. In addition, if the effective potential energy surface of the system is modeled by the semiempirical London-Eyring-Polanyi-Sato (LEPS) function, the correction is made directly in the Morse parameters for the two reactive bonds by adjusting the Sato parameters) , 19]. 

A generalization of the method of LONDON-EYRING-POLANYI-SATO (IiEPS) is proposed by J.POLAFYI /28/ for reactions involving three different atoms A,B,C by adjusting different values (S-, 82 S ) of the overlap integral for the three pairs of atoms (AB,AC,BC). 

The first and second columns of the Tables give the reaction and potential energy surface used. Standard abbreviations are employed for the names of the potential surfaces. Thus. PK = Porter-Karplus potential surface No 2 for H+H2. LSTH = Liu-Siegbahn-Truhlar-Horowitz potential surface for H+Hg. YLL = Yates-Lester-LIu potential surface for H+Hp. LEPS = extended London-Eyring-Polanyi-Sato potential surface and DIM = diatomics-in-molecules potential surface. 

The potential energy surface used for the CH4 + OH CH3 + H2O reaction combines an accurate potential function for H2O [31] with a London-Eyring-Polanyi-Sato (LEPS) function to describe the C-H and OH reactive bonds. The potential has accurate reactant and product ro-vibrational energy levels, correct bond dissociation energies and transition state geometries in reasonable accord with ah initio data [13,14]. It also incorporates the zero point energies of all modes not explicitly treated in the RBA calculations. 

London-Eyring-Polanyi-Sato potential energy surface No. 3 of Persky and Komweitz. 

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