Complete intermolecular potential surface

Intermolecular forces, sometimes called non-covalent interactions, are caused by Coulomb interactions between the electrons and nuclei of the molecules. Several contributions may be distinguished electrostatic, induction, dispersion, exchange that originate from different mechanisms by which the Coulomb interactions can lead to either repulsive or attractive forces between the molecules. This review deals with the ab initio calculation of complete intermolecular potential surfaces, or force fields, but we focus on dispersion forces since it turned out that this (relatively weak, but important) contribution took longest to understand and still is the most problematic in computations. Dispersion forces are the only attractive forces that play a role in the interaction between closed-shell ( 5) atoms. We will see how the understanding of these forces developed, from complete puzzlement about their origin, to a situation in which accurate quantitative predictions are possible. 

The complete intermolecular potential energy surface depends upon the intermolecular distance and up to five angles, as discussed in section Al.5,1.3. 

First, a complete description of the adsorbent is required this must include details of its solid structure, surface chemical structure, pore size and shape. One starts by assuming that the pores in the model adsorbent are all of the same size and shape and that they are unconnected. Secondly, the nature of the fluid-fluid and fluid-solid interactions must be precisely defined since the validity of the calculations is dependent on the accuracy of the intermolecular potential functions. 

Stratification, as illustrated by the plots in Figs. 5.4-5.G, is due to constraints on the packing of molecules next to the substrate surface and is therefore largely determined by the repulsive part of the intermolecular potential [38). Stratification is observed even in the complete absence of intermolecular attractions, such as in the case of a hard-sphere fluid confined between planar hard walls [165-167]. For this system Evans et al. [168] demonstrated that, as a consequence of the damped oscillatory character of the local density in the vicinity of the walls, is itself a damped oscillatory function of s, if s is of the order of a few molecular diameters, which is confirmed by the plot in Fig. 5.3. 

L hnear molecules, and A atoms are dictated by a multidimensional intermolecular potential energy surface. Find a general equation for the minimum number of coordinates necessary to completely describe this smface. Assume the molecules are completely rigid... 

For the interpretation of the measurements information on the structure of the clusters is very important. An ab initio calculation at one point of the total energy surface of a more than three-atom cluster including effects of correlation is a state-of-the-art task. A complete mapping of the surface is impossible. Therefore, we have used a model which is based on a reliable multi—center pair potential. Then the equilibrium geometries and total energy minima are determined by minimizing the intermolecular energy with respect to the molecular positions. To initiate a... 

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