Multiresolution algorithms for massively parallel molecular dynamics simulations of nanostructured materials

Abstract

Multimillion atom molecular-dynamics (MD) simulations are performed to investigate dynamics of oxidation of aluminum nanoclusters and properties and processes in nanostructured silicon carbide (n-SiC) and nanostructured amorphous silica (n-a- SiO2 ). The simulations are based on reliable interatomic interactions that include both ionic and covalent effects. The simulations are carried out on parallel architectures using highly efficient O(N) multiresolutions algorithms which include an adaptive load-balancing approach based on wavelets and a data-compression scheme based on fractals.Results from the oxidation simulation reveal a passivating amorphous oxide layer of thickness ∼ 40 Å, which is in excellent agreement with experiments. The oxide layer is amorphous and has mixed tetrahedral, Al(O1/4)4 , and octahedral, Al(O1/6)6 , configurations. The average mass density in the oxide region is 75% of the bulk alumina density. Local stresses in the oxide scale are analyzed and their correlation with the dynamics 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 simulation indicate the onset of sintering around 1500 K which is much lower than the 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 to 2 and their surface roughness exponents are ∼ 0.5. Pair-distribution functions and bond-angle distributions reveal a crystalline core and an amorphous interface in the consolidated n-SiC. In the case of nanophase silica glasses, the short-range order (SRO) is similar to that in the bulk glass but not the intermediate-range order (IRO). In the nanophase system the first sharp diffraction peak (FSDP), the signature of IRO, has a much smaller height and is shifted toward smaller k relative to the FSDP in the bulk system. The elastic moduli of nanophase silica glasses scale with the density as ∼ρ3.5 ; the bulk, shear and Young's moduli of n-SiC scale as ∼ρη , where η is 3.51±0.02 , 3.29±0.06 , and 3.34±0.03 , respectively.