We report on molecular-dynamics (MD) simulations of tensile loading of nano-crystalline Al modeled by an embedded-atom method (EAM) potential. Usage of two different sample preparation methods of the nano-crystalline material allows us to compare mechanical properties for different sample qualities. A Voronoi-constructed polycrystal exhibits nearly no pores and has different mechanical properties compared to a material that is sintered under pressure and temperature from spherical nanoparticles, resulting in a lower-density sample. We found an inverse Hall-Petch relation for the flow stress for grain sizes smaller than 10 nm. Intergranular fracture was observed for the larger Al grain sizes, but not for nano-crystalline Cu.

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Abstract. We review recent progress in understanding fundamental processes in biology, chemistry and physics on the basis of ab initio and molecular dynamics simulations. The first step of the visual process involving the excitation of bovine rhodopsin after absorption of light is taken as an example from biochemistry to demonstrate what is nowadays possible to simulate numerically. The act of freezing of water has recently been simulated, for the first time successfully, by scientists from chemistry. Martensitic transformation in bulk and nanophase materials, a typical and hitherto not completely solved problem from solid state physics, is used to illustrate the achievements of multimillion atoms simulations. Molecular Dynamics as a Multidisciplinary Numerical ToolMolecular dynamics (MD) has proved to be an optimum numerical recipe applicable to problems with many degrees of freedom from quite different fields of science. The knowledge of the energy or potential landscape of interacting particles, like electrons and atoms, enables one to calculate the forces acting on the particles and to study the evolution of the system with time. As long as classical mechanics is appropriate to describe the dynamics of the individual constituents (i.e. atoms or molecules), the Newtonian equations of motion can be related to the statistical mechanics of the (classical) particles by using the equipartition theorem, i.e. by combining the equationsfor i = 1 . . . N particles. Although the equipartition theorem holds only for classical particles, to the authors' knowledge the combination of classical and statistical physics has also been used to simulate small molecules at low temperatures without critically discussing so far the limitations of 9.1 and 9.2 when applying to very small quantum mechanical systems. The forces in 9.1 are then simply related to the gradients of the potential energy surface (PES) of either the classical or the quantum mechanical N -particle system. For pedagogical reasons let us recall the classical constant-temperature case. Omitting the statistical average in 9.2 means that the temperature is a measure

It has been conjectured that the local structure of simple monoatomic liquids is mainly of five-fold symmetry. Experimental evidence for such icosahedral building blocks has recently been found in liquid droplets of lead adjacent to a silicon wall and in deeply undercooled melts of pure metallic elements like bcc iron, fcc nickel and bcc zirconium. We have used molecular dynamics in order to investigate supercooling effects in the melt of another pure element (aluminum) on the basis of a common neighbor analysis. In the simulation we have employed an embedded atom method potential optimized with the help of ab initio calculations for aluminum. The simulations confirm the recent experimental results that, independent of the system, the icosahedral short-range order strongly increases with the degree of undercooling.