INTRODUCTION AND PERSPECTIVE

In the preceding chapters of this book we have dealt extensively with equilibrium properties of a wide variety of models and materials. We have emphasized the importance of insuring that equilibrium has been reached, and we have discussed the manner in which the system may approach the correct distribution of states, i.e. behavior before it comes to equilibrium. This latter topic has been treated from the perspective of helping us understand the difficulties of achieving equilibrium. The theory of equilibrium behavior is well developed and in many cases there is extensive, reliable experimental information available.

In this chapter, however, we shall consider models which are inherently non-equilibrium! This tends to be rather uncharted territory. For some cases theory exists, but it has not been fully tested. In other situations there is essentially no theory to rely upon. In some instances the simulation has preceded the experiment and has really led the way in the development of the field. As in the earlier chapters, for pedagogical reasons we shall concentrate on relatively simple models, but the presentation can be generalized to more complex systems.

DRIVEN DIFFUSIVE SYSTEMS (DRIVEN LATTICE GASES)

Over two decades ago a deceptively simple modification of the Ising lattice gas model was introduced (Katz et al., 1984) as part of an attempt to understand the behavior of superionic conductors.