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

United States. Dept. of Energy. Office of Basic Energy Sciences (Energy Frontiers Research Center. Award 2008LANL1026)

Design of Radiation Tolerant Materials Via Interface Engineering

Shock responses of nanoporous aluminum by molecular dynamics simulations

Study on wear behavior of FeNiCrCoCu high entropy alloy coating on Cu substrate based on molecular dynamics

Dynamic characterization of shock response in crystalline-metallic glass nanolaminates

Structural phase transformation in bulk single crystal Cu in different orientation under shock loading of different intensities has been investigated in this article. Atomistic simulations, such as, classical molecular dynamics using embedded atom method (EAM) interatomic potential and ab-initio based molecular dynamics simulations, have been carried out to demonstrate FCC-to-BCT phase transformation under shock loading of 〈100〉 oriented bulk single crystal copper. Simulated x-ray diffraction patterns have been utilized to confirm the structural phase transformation before shock-induced melting in Cu(100).

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A metastable phase of shocked bulk single crystal copper: an atomistic simulation study

Even though there are numerous experiments and molecular dynamic simulations of Cu under shock loading, there appears to be no literature on the evolution of different types of dislocation mechanisms and their mutual interactions during the process of shock loading, which this article addresses through molecular dynamic simulations using the Mishin EAM potential for Cu. Three different directions , , and that have been considered in this article are subjected to shock compression with piston velocities ranging between 0.3–3 km s−1. The evolution of Hirth locks, Lomer–Cottrell locks, cross-slips, jogs, and dislocation-originated stacking-fault tetrahedra are demonstrated in this article for different direction shock loading of single-crystal Cu.

https://iopscience.iop.org/article/10.1088/1361-651X/aa5850/pdf

Evolution of dislocation mechanisms in single-crystal Cu under shock loading in different directions

Non-equilibrium molecular-dynamic simulations were carried out on model three-dimensional nano-void copper material with different idealised pore structure and porosity to highlight differences in response behaviour between them when subjected to various piston velocities simulating planar shock loading of different intensities. This article demonstrates and explains from a mechanistic perspective the differences in response observed with respect to Hugoniot elastic limits, dislocation line and jet formation, void collapse mechanism and hot spot generation, specific volume, partial recrystallisation and temperature evolution in void collapsed regions, shock and particle velocity curves.

On shock response of nano-void closed/open cell copper material: Non-equilibrium molecular dynamic simulations

We have performed systematic molecular dynamics simulations to study the deformation behavior of a single crystal structure and a core-shell Cu@Ni nanoporous (NP) structure under shock loading for a wide range of shock intensities. Our results suggest that the core-shell structure exhibits less volume compression than the single crystal NP structure by virtue of its enhanced mechanical strength and associated interfacial strain-hardening under shock loading. The core-shell NP structure also demonstrates an increased shock-energy absorption efficiency of around 10.5% larger than the single crystal NP structure because of its additional Cu/Ni interface. The mechanisms of shock-induced deformation are observed to vary greatly with shock intensity. Pores are observed to collapse partially in both NP structures at very low shock intensity, up≤0.15 km/s. Complete collapsing of the pores through plastic deformation followed by direct crushing and formation of internal jetting and hot-spot have been observed at higher shock intensities. The evolution of microstructure and the underlying mechanisms operating at different shock intensity regimes have been investigated in this article. At a shock pressure of ∼6.05 GPa, i.e., up=0.75 km/s, the shock-induced deformed microstructure of both NP structures recovered through dynamic recrystallization. The postshock dynamic recrystallization has been observed to be mediated through rapid relaxation of shear stress followed by atomic rearrangements.

Anupam Neogi

Papers

A metastable phase of shocked bulk single crystal copper: an atomistic simulation study

Evolution of dislocation mechanisms in single-crystal Cu under shock loading in different directions

On shock response of nano-void closed/open cell copper material: Non-equilibrium molecular dynamic simulations

Atomistic simulations of shock compression of single crystal and core-shell Cu@Ni nanoporous metals

Twin-boundary assisted crack tip plasticity and toughening in lamellar γ-TiAl