Supermolecule approach to the intermolecular interactions in condensed media

5 SUPERMOLECULE APPROACH TO THE INTERMOLECULAR INTERACTIONS IN CONDENSED MEDIA 

As a general remark, in the calculations of the intermolecular interactions using the supermolecule approach, the size-extensivity of the methods applied is of crucial importance. Furthermore, the interaction energies calculated in the supermolecule approach usually suffer from what is called the basis set superposition error (BSSE), a spurious energy improvement resulting from the use of truncated basis sets. This error seems to be unavoidable in most practical calculations except for very small systems.  

The intermolecular interactions that correspond to the fixed geometry of the solute-solvent complex can be also studied by a perturbation approach. - It has been suggested that the perturbation theory has some advantages over the supermolecule approach and may therefore be considered conceptually more appropriate for the calculation of intermolecular interaction energies. In this case, the interaction energy is calculated directly and it may be separated into components of well-defined physical meaning. 

Within the direct reaction field (DRF) method,the classical part of the solute-sol-vent system (solvent) is treated as a distribution of the polarizable point dipoles, interacting with each other. The DRF Hamiltonian of the solute-solvent system is thus given by the following formula  

Numerous computational schemes have been developed to calculate the total molecular solvation energy or free energy using the combination of different theoretical solute-sol-vent interaction models. From these, one of the most popular is the SMx methodology. 

Suppan, N. Ghoneim, Solvatochromism, The Royal Society of Chemistry, London, 1997. 

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