LEPS method

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. 

Singlet and triplet imidogen have not yet been detected in solution by LEP methods. Future effort should be expended in this direction and it seems safe to predict that such work will be reported in the near future. 

It might be argued that the LEPS method is purely empirical in that none of the quantities that enter it are calculated and only the general form has some theoretical foundation. It has nevertheless been widely used in dynamical calculations to investigate the influence of certain features of the surface, such as the position and height of the transition state. 

A multidimensional PES for the solid-state reaction (9.19) has been calculated by Wight et al. [1993] with the aid of atom-atom potentials combined with the semiempirical LEPS method (see, e.g., Eyring et al. [1983]). Because of the substantial exoergicity of this elementary step, the... 

A semi-empirical extension of the London equation—the LEPS method—allows for a simple but somewhat crude construction of potential energy surfaces. 

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. 

The LEPS method is also used for general triatomic systems. Here equations that are equivalent to Eqs (3.37) and (3.38) are written down and solved for the other diatomic pairs (AC and BC). The LEPS method provides a quick but somewhat crude estimate of potential energy surfaces. 

One of the first semi-empirical methods developed for potential energy calculations is the London, Eyring and Polanyi (LEP) method. The basic approximations are ... 

Sato modified the LEP method, and the resulting semi-empirical method is known as LEPS. Sato uses the Morse potential for the attractive potential. For the repulsive potential one uses the expression... 

Semiempirical potential energy calculations of triatomic reactive systems are usually carried out using either the London equation, as in the London-Eyring-Polanyi-Sao (LEPS) method, ... 

We shall present results for several kinds of potential energy surfaces. Many of the surfaces are obtained by the London-Eyring-Polanyi-Sato (LEPS) method, involving a single adjustable (Sato) parameter, or by the extended LEPS method, in which different Sato parameters are used for different atomic pairs. These methods are reviewed elsewhere.For other calculations we used rotated Morse curves (RMC),semiempirical valence bond (VB) surfaces, and rotated-Morse-bond-energy-bond-order (RMBEBO) surfaces. 

When the above procedure is done for the first time, the activation energy calculated from Eq. (3.60) will not be the same as the experimental value. One can adjust p and p in the BEBO method or A in the LEPS method to get these to agree, after which the preexponential factor according to TST is fixed. 

---