doi:10.1016/j.cpc.2007.02.097
Copyright © 2007 Published by Elsevier B.V.
Multimillion atom simulations of dynamics of wing cracks and nanoscale damage in glass, and hypervelocity impact damage in ceramics
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Priya Vashishtaa, Rajiv K. Kaliaa and Aiichiro Nakano
, a, 
aCollaboratory for Advanced Computing and Simulations, Department of Chemical Engineering and Materials Science, Department of Physics and Astronomy, Department of Computer Science, University of Southern California, Los Angeles, CA 90089-0242, USA
Available online 6 March 2007.
Abstract
We have developed scalable parallel algorithms for first-principles based predictive atomistic simulations of materials. We have achieved parallel efficiency 0.998 for 134 billion-atom molecular dynamics (MD), 1.06 billion-atom reactive force-field MD, and 11.8 million-atom (1.04 trillion electronic degrees-of-freedom) quantum-mechanical MD in the framework of the density functional theory on 131,072 BlueGene/L processors. We have performed up to 540 million-atom MD simulations to study: (1) initiation, growth and healing of wing cracks in confined silica glass; and (2) damage initiation during hypervelocity impact on advanced ceramics.
Keywords: Molecular dynamics; Quantum mechanics; Density functional theory; Parallel computing; Wing cracks; Hypervelocity impact
Fig. 1. Benchmark tests of reactive and nonreactive MD simulations on 131,072 BlueGene/L processors. The execution time per MD step is shown as a function of the number of atoms for: quantum-mechanical MD based on the embedded divide-and-conquer density functional theory (EDC-DFT, circles); fast reactive force-field MD (F-ReaxFF, squares); and nonreactive space–time multiresolution MD (MRMD, triangles). Lines show O(N) scaling.
Fig. 2. Snapshots of void coalescence causing fracture in silica glass: (a) Initial MD configuration with two voids of diameter 3 nm each, separated by 3 nm; (b) formation of nanovoids in the inter-void region; (c) a ligament connecting the two voids and nanoscale cracks on the void surfaces at an applied strain of 7%; and (d) failure caused by void coalescence and damage spreading through the glass at a strain of 11.2%.
Fig. 3. Snapshots of the wing crack and nanocavities. (Right) wing crack turned in the direction of the applied load. (Middle) a large cavity (red) splits off the wing crack. (Left) after 4 ps the wing crack and the cavity rejoin and the crack recedes by 6 nm. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
Fig. 4. A thin slice of a 540 million-atom alumina target 40 nm in front of the projectile during hypervelocity impact simulation. Deviation in the number of 6-member rings from perfect crystalline atoms (blue) is color-coded using the gradient bar above. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
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