Clusters: An Introduction

Abstract

Physicists and chemists are used to label quite different things with the term “cluster”. Therefore, to avoid confusion, we will in the context of this Volume assign a group (or an accumulation) of atoms or molecules in the gas phase, held together by weak intermolecular forces, as a cluster. In that sense, clusters represent the link between the gaseous and condensed phase. It is well known since the work of van der Waals1 that the existence of the condensed phase stems from the forces between molecules. Therefore, these forces are commonly referred to as van der Waals forces and, consequently, an accumulation of atoms or molecules is labelled as a van der Waals cluster. Although at the time of van der Waals the origins of such weak and short range intermolecular forces were not understood, the fundamental relation between the macroscopic properties of matter and the forces between the constituent molecules was already evident.