Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Fast parallel algorithms for short-range molecular dynamics

https://hal.archives-ouvertes.fr/hal-01513346/document

Isogeometric analysis : CAD, finite elements, NURBS, exact geometry and mesh refinement

Mechanical properties of nanocrystalline materials

Deformation twinning in nanocrystalline materials

Three strategies to achieve uniform tensile deformation in a nanostructured metal

To elucidate the mechanisms of grain growth in nanocrystalline fcc metals, we have performed fully three-dimensional molecular-dynamics simulations with a columnar grain structure and an average grain diameter of 15 nm. Based on the study of coarse-grained materials, the conventional picture is that grain growth is governed by curvature-driven grain-boundary migration. However, our simulations reveal that in a nanocrystalline material grain rotations play an equally important role, at least during the early stages of grain growth. By eliminating the grain boundary between neighboring grains, such rotations lead to grain coalescence and the consequent formation of highly elongated grains. A detailed analysis exposes an intricate coupling between this mechanism and the conventional grain-boundary-migration dominated mechanism. Incorporation of these insights into mesoscopic models should enable more realistic mesoscopic simulations of grain growth in nanocrystalline materials. (A short movie showing the overall evolution of the grain microstructure can be viewed at http://www.msd.anl.gov/im/movies/graingrowth.html.)

Mechanisms of grain growth in nanocrystalline fcc metals by molecular-dynamics simulation.

Stress-enhanced grain growth in a nanocrystalline material by molecular-dynamics simulation

Recent investigations of grain growth in nanocrystalline materials have revealed a new growth mechanism: grain-rotation-induced grain coalescence. Based on a simple model employing a stochastic theory and using computer simulations, here we investigate the coarsening of a polycrystalline microstructure due solely to the grain-rotation coalescence mechanism. Our study demonstrates that this mechanism exhibits power-law growth with a universal scaling exponent. The value of this universal growth exponent is shown to depend on the assumed mechanism by which the grain rotations are accommodated.

Dorel Moldovan

Papers

Mechanisms of grain growth in nanocrystalline fcc metals by molecular-dynamics simulation.

Stress-enhanced grain growth in a nanocrystalline material by molecular-dynamics simulation

Scaling behavior of grain-rotation-induced grain growth.

Theory of diffusion-accommodated grain rotation in columnar polycrystalline microstructures

Rapid microwave-assisted biomass delignification and lignin depolymerization in deep eutectic solvents