Multiresolution algorithms for massively parallel molecular dynamics simulations of nanostructured materials

Multimillion atom molecular-dynamics (MD) simulations are performed to inve stigate dynamics of oxidation of aluminum nanoclusters and properties and p rocesses in nanostructured silicon carbide (n-SiC) and nanostructured amorp hous silica (n-a-SiO2). The simulations are based on reliable interatomic i nteractions that include both ionic and covalent effects. The simulations a re carried out on parallel architectures using highly efficient O(N) multir esolutions algorithms which include an adaptive load-balancing approach bas ed on wavelets and a data-compression scheme based on fractals. Results from the oxidation simulation reveal a passivating amorphous oxide layer of thickness similar to 40 Angstrom, which is in excellent agreement with experiments. The oxide layer is amorphous and has mixed tetrahedral, A l(O-1/4)(4), and octahedral, Al(O-1/6)(6). configurations. The average mass density in the oxide region is 75% of the bulk alumina density. Local stre sses in the pride scale are analyzed and their correlation with the dynamic s of oxidation is determined. Sintering, structural correlations, and mechanical behavior of n-SiC and n- a-SiO2 are investigated. In the case of n-SiC, both experiment and simulati on indicate the onset of sintering around 1500 K which is much lower than t he sintering temperature for coarse-grained SiC. In both n-SiC and n-a-SiO2 , pores are found to be self-similar. They have a fractal dimension close t o 2 and their surface roughness exponents are similar to 0.5. Pair-distribu tion functions and bond-angle distributions reveal a crystalline core and a n amorphous interface in the consolidated n-SiC. In the case of nanophase s ilica glasses, the short-range order (SRO) is similar to that in the bulk g lass but not the intermediate-range order (IRO). In the nanophase system th e first sharp diffraction peak (FSDP), the signature of IRO, has a much sma ller height and is shifted toward smaller k relative to the FSDP in the bul k system. The elastic moduli of nanophase silica glasses scale with the den sity as similar to rho(3.5); the bulk, shear and Young's moduli of n-SiC sc ale as similar to rho(eta), where eta is 3.51 +/- 0.02, 3.29 +/- 0.06, and 3.34 +/- 0.03, respectively. (C) 2000 Elsevier Science B.V. All rights rese rved.