INTRODUCTION TO THEORETICAL APPROACHES TO CHEMISORPTION

We present in this paper different theoretical approaches to chemisorp tion. Our goal is not to review all the approaches and discuss the met hods, but to select some studies, emphasizing the point of view of the chemist that chemisorption may be interpreted locally around the adso rption site. However, models may be finite (clusters, finite cube) or infinite (periodic systems). In contrast to molecular systems (and to organometallic clusters) whose structures are ruled by an accurate ele ctron count, small variations of the number of electrons in the unit c ell have little effect on infinite metallic systems. The role of s, p and d valence orbitals in metals is discussed. Finally several problem s concerning the surface are investigated: the influence of the coordi nation of the surface atoms, the reconstruction, the acidity/basicity of the active sites, the lateral interactions between absorbates and t he adsorption of molecules through several functions at the same time. (C) 1998 Elsevier Science B.V.