The procedure and steps presented above is important when dealing with nanosystems composed of up to a few hundred atoms and molecules, or macro- and supra-molecules for which potential functions are not available. To study nanostructures composed of several hundred to several million atoms or molecules including macroscopic systems, the computationally most efficient method is the use of phenomenological interatomic and intermolecular potentials.

The phenomenological potentials are obtained by using empirical approaches of selecting a mathematical function and fitting its unknown parameters to various, experimentally determined, properties of the system, such as its lattice constant.

Interatomic and intermolecular potentials must be able to model the energetics and dynamics of nanostructures, and this fact lies at the very foundation of the computer-based modeling and simulations. The significance of much of the modeling and simulation results, their accuracy and the extent to which they represent the real behavior of nanostructures, and their transitions, under varied conditions, depends in a critical manner on the accuracy of the interatomic and intermolecular potentials employed.

A great deal of effort has been spent over the years to develop phenomenological intermolecular potentials to model the bonding in various classes of materials, such as metallic, semi-metallic, semiconducting, and organic atoms and molecules. For a review see [10,69-71].

To be effective for computational nanotechnology, interatomic and intermolecular potentials must possess the following properties [10,72,73]:

1. Flexibility: A potential energy function must be sufficiently flexible that it could accommodate as wide a...