Introduction

This chapter provides the introductory appetizer and aims to leave the reader new to MD with a feeling for what the subject is all about. Later chapters will address the techniques in detail; here the goal is to demonstrate a working example with a minimum of fuss and so convince the beginner that MD is not only straightforward but also that it works successfully. Of course, the technique for evaluating the forces discussed here is not particularly efficient from a computational point of view and the model is about the simplest there is. Such matters will be rectified later. The general program organization and stylistic conventions used in case studies throughout the book are also introduced.

Soft-disk fluid

Interactions and equations of motion

The most rudimentary microscopic model for a substance capable of existing in any of the three most familiar states of matter – solid, liquid and gas – is based on spherical particles that interact with one another; in the interest of brevity such particles will be referred to as atoms (albeit without hint of their quantum origins). The interactions, again at the simplest level, occur between pairs of atoms and are responsible for providing the two principal features of an interatomic force. The first is a resistance to compression, hence the interaction repels at close range. The second is to bind the atoms together in the solid and liquid states, and for this the atoms must attract each other over a range of separations.