Coulomb integrals potential energy surfaces

Although the underlying approximations are too crude to obtain an accurate potential energy surface, another very important observation can be made when the London equation is compared to the energy expression for H2 the total energy is not equal to the sum of pairwise H-H interactions. Thus, E(Rab, Rac, Rbc) Z Eab + Eac + Ebg, where Eab corresponds to E+ of Eq. (3.31), and Eac and Ebc are given by similar expressions. The simple summation of pairwise H-H interactions only holds for the Coulomb integrals ... 

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. 

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