Submicron-scale thermics - Introduction to molecular dynamics

Molecular dynamics (MD) is a numerical technique for simulating the behavior of materials on an atomic scale. Since the end of the Second World War, this technique has enjoyed a boom over the years, directly linked to improvements in computer performance. Molecular dynamics is used in research. It is used to study and predict the physical, chemical and mechanical properties of materials under conditions that make experimental observation very difficult, if not impossible: too small a spatial scale, extremely rapid phenomena, very high temperatures and pressures, hazardous materials (radioactive, corrosive).

New technologies make it possible not only to study matter at the atomic scale, but also to shape it into electronic, optical, thermal and mechanical nanocomponents. Today's computers and software make molecular dynamics a readily accessible tool. Researchers and engineers now have the experimental and theoretical resources they need to meet the major challenges of nanotechnology. With regard to heat transfer, they need to master :

• conductive heat transfer in semiconductors and composite materials;

• heat exchange in two- and three-phase systems (evaporation, condensation and meniscus formation);

• heat transfer phenomena at the interface between solids in contact ;

• the processes used to produce materials, so that their properties can be perfectly controlled.

The aim of this article is to take you behind the scenes of molecular dynamics. For the engineer, it's a question of understanding the fundamentals of molecular dynamics in order to judge its usefulness and potential applications. The technique itself is relatively simple and easy to apply. Molecular dynamics is based on the integration of Newton's fundamental equation of dynamics. Some of the most common integration schemes are presented here. The basic principles for implementing molecular dynamics are explained. However, if only this aspect of molecular dynamics were addressed, many of the questions that need to be asked for a serious study would be omitted. In simple terms, molecular dynamics is a step in the process of simulating matter:

• upstream, the determination and choice of interaction potentials. This point is discussed to highlight the limitations of molecular dynamics. In theory, the potential for a given element is unique. It can be used to simulate matter in all its states: solid, liquid, gaseous, crystalline or amorphous. In fact, potentials are designed to best simulate matter for a specific purpose, resulting in different potentials for the same element;

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