1.09.1 Introduction

A concept that is fundamental to the foundations of Comprehensive Nuclear Materials is that of microstruc­tural evolution in extreme environments. Given the current interest in nuclear energy, an emphasis on how defects in materials evolve under conditions of high temperature, stress, chemical reactivity, and radiation field presents tremendous scientific and technological challenges, as well as opportunities, across the many relevant disciplines in this important undertaking of our society. In the emerging field of computational science, which may simply be defined as the use of advanced computational capabilities to solve complex problems, the collective contents of Comprehensive Nuclear Materials constitute a set of compelling and specific materials problems that can benefit from science-based solutions, a situation that is becoming increasingly recognized.1-4 In discus­sions among communities that share fundamental scientific capabilities and bottlenecks, multiscale modeling and simulation is receiving attention for its ability to elucidate the underlying mechanisms governing the materials phenomena that are critical to nuclear fission and fusion applications. As illu­strated in Figure 1, molecular dynamics (MD) is an atomistic simulation method that can provide details of atomistic processes in microstructural evolution.

As the method is applicable to a certain range of length and time scales, it needs to be integrated with other computational methods to span the length and time scales of interest to nuclear materials.9

The aim of this chapter is to discuss in elemen­tary terms the key attributes of MD as a principal method of studying the evolution of an assembly of atoms under well-controlled conditions. The intro­ductory section is intended to be helpful to students and nonspecialists. We begin with a definition of MD, followed by a description of the ingredients that go into the simulation, the properties that one can calculate with this approach, and the reasons why the method is unique in computational materials research. We next examine results of case studies obtained using an open-source code to illustrate how one can study the structure and elastic properties of a perfect crystal in equilibrium and the mobility of an edge dislocation. We then return to Figure 1 to provide a perspective on the potential as well as the limitations of MD in multiscale materials modeling and simulation.