Additivity of intermolecular

Theoretical considerations based upon a molecular approach to solvation are not yet very sophisticated. As in the case of ionic solvation, but even more markedly, the connection between properties of liquid mixtures and models on the level of molecular colculations is, despite all the progress made, an essentially unsolved problem. Even very crude approximative approaches utilizing for example the concept of pairwise additivity of intermolecular forces are not yet tractable, simply because extended potential hypersurfaces of dimeric molecular associations are lacking. A complete hypersurface describing the potential of two diatomics has already a dimensionality of six In this light, it is clear that advanced calculations are limited to very basic aspects of intermolecular interactions,... 

Subsequently, a kinetic theory of intercollisional interference was developed (Lewis 1980 and 1985). The kinetic theory was based on the idea of pairwise additivity of intermolecular force and induced dipole moment. It traces the collisional history of an individual molecule of a highly diluted system. The traced molecule may be a vibrating molecule, surrounded by non-vibrating molecules, or else a dissimilar molecule of low concentration (gas mixtures). 

Fowkes FM. (1963). Additivity of intermolecular forces at interfaces. L Determination of the contribution to surface and interfacial tensions of dispersion forces in various liquids. / Phys Chem 67 2538-2541. 

Certainly, the discrete SWB model is rather crude. It does not take into account the long-range nature of Coulomb interaction, although it is of great significance for aqueous systems. Moreover, this model does not consider molecules polarizability and other effects related to the non-additivity of intermolecular interaction. Therefore it is quite surprising to observe a close correlation between the theoretical predictions based on the SWB model and contemporary quantum-chemical calculations. Some of the coincidences are listed below. 

Surface tensions, interfacial tensions, and contact angles can be used as laboratory tools for the evaluation of the various intermolecular forces that determine cohesion in a single phase or adhesion between two dissimilar materials at an interface. By the use of these tools, considerable information about the magnitude of various intermolecular forces may become available. Basic understanding of means to determine interfacial forces has sprung from the principle of additivity of intermolecular forces at surfaces and interfaces [4, 6]. 

The calculation methods of the solubility parameters for polymers have an advantage over experimental methods that they do not have any prior assumptions regarding interactions of polymer with solvents. The numerous examples of good correlation between calculated and experimental parameters of solubility for various solvents support the assumed additivity of intermolecular interaction energy. 

ABSTRACT Ground state properties of several conceivable hydrogen bonded trimers composed of HCN and HP molecules have been evaluated at the SCP level. The most stable ones of these trimeric complexes have subsequently been reinvestigated with electron correlation methods (ACPP). We provide a survey of stabilization energies, dipole moments, selected harmonic vibrational frequencies and corresponding infrared intensities. We also discuss various aspects of the non-additivity of intermolecular interaction taking place in these clusters. 

F. M. Fowkes, Determination of interfacial tensions, contact angles.and dispersion forces in surfaces assuming additivity of intermolecular interactions in surfaces. J. Phys. Chem. 66,382 (1962). 

---