Extended Hiickel theory binding energies

In Eq. (10.9), is the overlap energy and S the corresponding overlap between adsorbate and surface atomic orbitals. Approximate Eq. (10.9) applies when ad molecule orbitals are s-symmetric and the metal electrons are also described by s-atomic orbital. Equation (10.9) is a familiar expression within molecular orbital theory and is deduced from tight binding theory including overlap of the atomic orbitals as in extended Hiickel theory (Hoffmann) is used [9]. 

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