Why Nonequilibrium Molecular Dynamics

We begin this chapter by making it clear that equilibrium molecular dynamics techniques are important. The methodology of dynamics, per se, has 

Reviews in Computational Chemistry, Volume 14 Kenny B. Lipkowitz and Donald B. Boyd, Editors Wiley-VCH, John Wiley and Sons, Inc., New York, 2000 

One easy extension of equilibrium molecular dynamics is the computation of the properties of condensed matter systems in the presence of external fields. Many experiments are done by applying an external field, whether it be an electric field, heat gradient, or some type of flow. Usually, the experimentalist waits some time for the system under investigation to reach a steady state in the presence of the applied field. Measurements are then performed to deduce structural or dynamical information. Performing this task on a computer is what is commonly known as nonequilibrium molecular dynamics (NEMD). It is nonequilibrium in the sense that, in the presence of an external field, the system at the steady state will be in a state of lower entropy. Upon removing the external field, the system will return to the state of maximum entropy or the equilibrium state. 

Equilibrium molecular dynamics was put on a firm theoretical ground with Andersen s seminal paper on extended system dynamics (to be discussed in great detail later). NEMD found its first success in this area with the advent of the so-called DOLL s (not an acronym) algorithm by Hoover and coworkers.  

Finally, with the advent of high speed computers, parallel architecture, and the popularity of extended system methods, NEMD has seen yet another resurgence. Researchers are beginning to access the resources that allow one to compute the physical properties of real lubricants. The aim of this chapter is to provide the theoretical and technical foundations to enable simulators to model realistic systems under nonequilibrium conditions. 

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