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

Molecular dynamics simulation of laser assisted grinding of GaN crystals

Three-dimension molecular dynamics (MD) simulation is employed to investigate the nanoscratching process of monocrystalline silicon with diamond tools. The effects of tool geometry on subsurface damage and scratching surface integrity are investigated by analyzing phase transformation, chip, defect atoms, hydrostatic stress, von Mises stress and workpiece deformation. In addition, a theoretical analytical model to study the subsurface damage mechanism by analyzing the zone size of phase transformation and normal force with diamond tools at different half-apex angles on silicon surfaces is established. The results show that a bigger half apex angle causes a higher hydrostatic stress, a larger chip volume, a higher temperature and a higher potential energy, and increases subsurface damage. The results also reveal that the evolution of crystalline phases is consistent with the distribution of hydrostatic stress and temperature. In addition, tip scratching with a bigger half-apex angle would result in a large...

https://journals.sagepub.com/doi/pdf/10.1177/1350650118765351

Molecular dynamics simulation of subsurface damage mechanism during nanoscratching of single crystal silicon

A study of ultraprecision mechanical polishing of single-crystal silicon with laser nano-structured diamond abrasive by molecular dynamics simulation

Surface integrity of parts can seriously be damaged by mechanical and thermal loads during machining leading to crack initiation, constraining of parts or damage. At present, it is very difficult to observe the diverse nanoscale physical phenomena occurring through experiments due to in-process measurement problems, inaccessible contact area of tool and workpiece, and the difficulty of surface analysis at this range. Therefore, more insight is needed, which on the long run will help to achieve high precision manufacturing with predictability, repeatability, and productivity. The most logical method presently is to explore available simulation techniques. Of the many methods of simulation, atomistic simulation methods have proven to be suitable techniques for modeling at the nanoscale. Molecular dynamics (MD) is a comprehensive physical model that contains inherent information such as geometry, velocities, and forces which can be used to derive others like energy, temperature, and stresses, thereby providing support to a wider range of engineering problems such as simulations of ductile and brittle materials. This paper is aimed at reviewing journals on the use of classical MD method (corroborating it with experimental findings) for nanoscale machining of silicon with references to its use in nanomachining of other metals when necessary.

Review of molecular dynamics/experimental study of diamond-silicon behavior in nanoscale machining

Molecular dynamics is employed to study the mechanism of material removal and subsurface damage of monocrystalline silicon when it is under a nanoscale high-speed laser-assisted grinding of a diamond tip. Laser-assisted machining (LAM) is that the workpiece is locally heated by an intense laser beam before material removal. The effects of laser moving speed, laser pulse intensity and laser spot radius are thoroughly investigated in terms of atomic trajectories, phase transformation, temperature distribution, grinding temperature, grinding force and friction coefficient. The investigation shows that a higher laser moving speed reduces the subsurface damage and improves the material remove rate because of fewer atoms with five and six coordination atoms and more chips. Besides, both tangential grinding force (Fx) and normal grinding force (Fy) decrease as the laser moving speed increases. The distribution of high-temperature zone strongly depends upon the effect of laser pulse intensity and laser sp...

Genyu Chen

Papers

A molecular dynamics investigation into the mechanisms of material removal and subsurface damage of nanoscale high speed laser-assisted machining