Multimillion Atom Reactive Simulations of Nanostructured Energetic Materials

For large-scale atomistic simulations involving chemical reactions to study nanostructured energeticmaterials, we have designed linear-scaling molecular dynamics algorithms: 1) first-principles-based fast reactive force field molecular dynamics, and 2) embedded divide-and-conquer density functional theory on adaptive multigrids for quantum-mechanical molecular dynamics. These algorithms have achieved unprecedented scales of quantummechanically accurate and well validated, chemically reactive atomistic simulations [0.56 billion-atom first principles-based fast reactive force field molecular dynamics and 1.4 million-atom (0.12 trillion grid points) embedded divide-and-conquer density functional theory molecular dynamics] in addition to 18.9 billion-atom nonreactive space-time multiresolution molecular dynamics, with parallel efficiency as high as 0.953 on 1920 Itanium2 processors. These algorithms have enabled us to perform reactive molecular dynamics simulations to reveal various atomistic processes during 1) the oxidation of an aluminum nanoparticle, 2) the decomposition and chemisorption of an RDX (1, 3, 5-trinitro-1, 3, 5-triazine) molecule on an aluminum surface, and 3) shock-initiated detonation of energetic nanocomposite material (RDX crystalline matrix embedded with aluminum nanoparticles.