Potential Energy Functional Forms

Concomitant with these developments in spectroscopy, thermochemists were finding that, to a reasonable approximation, molecular enthalpies could be determined as a sum of bond enthalpies. Thus, assuming transferability, if two different molecules were to be composed of identical bonds (i.e., they were to be isomers of one kind or another), the sum of the differences in the strains of diose bonds from one molecule to the other (which would arise from different bond lengths in the two molecules - the definition of strain in this instance is the positive deviation from the zero of energy) would allow one to predict the difference in enthalpies. Such prediction was a major goal of the emerging area of organic conformational analysis. 

The rest of this chapter examines the various components of the molecular energy and the force-field approaches taken for their computation. The discussion is, for the most part, general. At the end of the chapter, a comprehensive listing of reported/available force fields is provided with some description of their form and intended applicability. 

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Much can be said about the details of these simulations, including issues such as potential energy function form and parameterization [8-14], simulation conditions, treatment of long-range interactions [1, 2], the correct ensemble to simulate, and the proper timescales of the simulations. However, much of this is published already and here we will concentrate on the results of these studies which illustrate how small molecules move in and through the bilayer. 

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