Preface

This book is focussed on the theory and modelling of dispersion forces. These emergent electromagnetic forces affect all matter containing electrons, are primarily attractive, and are often described as weak though their effects can be dominant, just as is the case for gravity, another weak attractive force.

There are various texts^1–6  dealing with dispersion interactions, primarily from the macroscopic, field-oriented viewpoint. These works typically treat the matter as a bulk dielectric medium. This approach has been very successful for small but essentially macroscopic objects, such as in colloids, including cases where they are in close but non-intimate contact such as in adhesion of paints. These macroscopic approaches do not, however, cover in detail the interactions down to intimate contact where atomic-level, chemical and solid-state physics properties of the interacting pieces of matter are important. Referring to these macroscopic approaches as applied to intimate contact, Adrian Parsegian says on page 35 of his book:⁶  “these are at best approximations and at worst only mind games”. This region of intimate contact is very important and is a major focus of this book. To treat it properly we are led into some fairly challenging areas of quantum chemistry and condensed matter physics involving significant numerical computation. Reliable, computable predictive methods are only beginning to appear.

There are also a number of chemically oriented texts^7–9  on intermolecular interactions in general, with dispersion interactions of course included.

However, not much is available with an exclusive focus on dispersion forces, including realistic treatment of atoms, molecules, nano-structures and bulk matter. This coverage requires both the coarse-grained and fine-grained levels of description. This is the scope of the present book.

We aim to cover the physics, chemistry and mathematics of dispersion forces, starting from qualitative ideas, and a minimal undergraduate knowledge of mathematics and science, and developing all approaches up to the current state of the art. A synthesis of physical and chemical approaches is required in order to provide a seamless coverage of these interactions at all separations between the interacting bodies.

This is a very large area to cover, and in order to do so we have decided to provide only minimal coverage of the effects of electromagnetic retardation or thermal effects on the electromagnetic field itself, as these are very well covered in many texts and are typically not dominant in the near-contact regime where we largely concentrate. This typically limits us to inter-system separations less than about a micron, which is in fact where much of the current interest lies for technologies and devices.

The book is organised as follows. The first two chapters give a general and historical introduction, followed by an outline of the major phenomena and concepts, at a simple and highly intuitive level. The next few chapters present the major theoretical methods in some detail, starting from a relatively low level and building up to the state of the art. Then there are some chapters briefly discussing application areas of the various methods, emphasising cases not adequately covered by the traditional macroscopic dispersion approaches. A summary chapter suggests practical software choices for modelling dispersion forces in various application areas. Finally the appendices develop some relevant mathematics and physics topics that are probably not familiar at the lower-year undergraduate level.