Multimillion to Billion Atom Simulations of Nanostructured Materials Under Extreme Conditions

Priya Vashishta, Rajiv K. Kalia and Aiichiro Nakano

Collaboratory for Advanced Computing and Simulations (CACS) Departments of Chemical Engineering & Materials Science, Physics, and Computer Science

University of Southern California, Los Angeles, CA 90089-0242, USA Email: (priyav, rkalia, anakano)@usc.edu

Molecular dynamics (MD) simulations are performed to study critical issues in the area of

structural and dynamical correlations, and reactive processes in nanostructured materials under extreme conditions. Scalable space-time multiresolution algorithms implemented on multi-teraflop to petaflop computers enable large-scale MD simulations involving multimillion to multibillion atoms. We report the results for (1) our linear scaling simulation algorithms; and MD simulations of (2) CdSe nanorods embedded in a liquid undergoing forward and reverse structural phase transformation under hydrostatic pressure; (3) electric field-induced switching of poly ethylene glycol (PEG) terminated self-assembled monolayers (SAMs); (3) dynamic fracture in a nanocomposite consisting of SiO2 coated SiC fibers in a Si3N4 matrix; (4) hypervelocity projectile impact damage in AlN and strong interplay between shock-induced structural phase transformation, plastic deformation and brittle cracks.

Keywords: Molecular Dynamics, o(N) Algorithms, Nanorods, SAMs, Hypervelocity impact

Fig. 1: Execution times of our MD, reactive MD and density functional theory algorithms on 131,072 BlueGene/L processors, 1,920 Itanium2 processors, and 2,000 Opteron cores.

Fig. 2: Our MD simulation of a CdSe nanorod immersed in fluid.

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AMTC Letters Vol. 1 (2008)

© 2008 Japan Fine Ceramics Center

Fig. 3: The atomic configuration color coded by charges: oxygen (red), hydrogen (white), methyl terminal carbon (yellow) and carbon in PEG (green) in top 6Å layer, with the applied electric filed of (a) Ez = 0 and (b) Ez = 2 V/Å.

Fig. 4: Fracture of a 1.5-billion atom fiber reinforced ceramic composite. (Left) Si3N4 (red) ceramic reinforced with silica-coated SiC fibers (yellow). (Right) Atomistic model of fractured Si3N4 matrix reinforced with SiC fibers coated with amorphous silica. Small spheres represent Si atoms, and large spheres represent N (green), C (magenta), and O (cyan) atoms.

Fig. 5: Our MD simulation of hypervelocity impact on a ceramic material has uncovered new damage initiation mechanisms arising from the interplay of shock waves and structural phase transformation.

143

AMTC Letters Vol. 1 (2008)

© 2008 Japan Fine Ceramics Center