Body and Molecular Surface

Molecular surface is one such concept, derived from macroscopic analogies, where some of the quantum mechanical aspects of molecules are often disregarded. The approximate nature of the model, however, does not lessen its value in many practical applications, as long as its limitations are well recognized. The molecular surface concept is very useful for the interpretation of molecular size and shape properties within approximate models. 

However, it is possible to construct both classical and approximate quantum chemical molecular models within which molecular surface can be defined by requiring only that this surface enclose the essential part of the molecule, and a variety of computational methods are available for the detailed, nonvisual study of the shapes of these molecular surfaces. There are various criteria for what is to be considered the essential part, and below we shall review some of the more frequently applied choices. 

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Molecules are three-dimensional objects and they do occupy some space. When considering the space requirements of molecules, it is natural to associate with them a formal molecular body and a formal molecular surface [84-88]. In a simplistic model, this surface is a formal molecular boundary, a closed surface that separates the 3D space into two parts the molecular body enclosed by the surface that is supposed to represent the entire molecule, and the rest of the 3D space that falls on the outside of the surface, hence on the outside of the molecule. The above, intuitive concepts of molecular body and molecular surface are very useful for the interpretation of molecular size and shape properties within approximate models. 

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