1. Concept definition

Aggregates are particles made up of a limited number of atoms or molecules (hereinafter referred to as components), linked by various bonds. They range from aggregates composed of two atoms to those containing several hundred atoms.

It's not easy to define what an aggregate is, because there's no rigorous definition, and in particular, it's relatively difficult to distinguish precisely what is an aggregate and what is a molecule. Let's take the case of a C60 carbon aggregate ("foot-ballene"); it is an aggregate, but it has the main properties that characterize...