The history of physics furnishes many examples of how a simple semiem pirical method, essentially based on intuitive considerations, may prove to be much more successful than a rigorous theoretical approach. A pertinent example is the method of atom-atom potentials, which treats the intermolec ular interactions between polyatomic molecules in terms of pairwise inter actions between their constituent atoms. Despite a few conceptual short comings, the method provides a fairly reliable practical means of handling, on a microscopic level, a wide range of problems that arise in the solid-state...