Chapter 2.1 Computer simulation of adsorption on amorphous oxide surfaces

Abstract

Publisher Summary The understanding of adsorption on amorphous oxide surfaces is important because the surfaces of almost all high specific surface area adsorbents are strongly heterogeneous. This means that isotherms, heats, and other characteristics of adsorption on those surfaces deviate considerably from what is expected on theoretical grounds for homogeneous surfaces, which can be either single faces of ideal crystals or more idealized, absolutely smooth surfaces. Evidently, the degree of adsorption heterogeneity in a given system depends upon both the adsorbent and the adsorbate. For the simplest molecules like argon, it is generally believed that the adsorption heterogeneity is often just a manifestation of the irregularity of the surface atomic structure. To carry out computer simulations of physical adsorption on an amorphous oxide, the irregular (amorphous) atomic structure at its surface has to be simulated. This may be done in several ways. One of these directly models the formation of vitreous silica from the liquid. The first stage of this procedure is a molecular dynamics computer simulation of liquid SiO2, which presupposes an adequate modeling of the essentially covalent forces between constituent atoms. Thus, this chapter first reviews the modeling of these interatomic forces. The next stage can consist of the simulation of rapid cooling (quenching) of this liquid. This, as well as other methods of computer simulation of amorphous oxide surfaces, is discussed in this chapter.