Andrey Omeltchenko

Sintering, structure and mechanical properties of nanophase SiC: a molecular dynamics and neutron scattering study

Structure, mechanical properties, and sintering of nanostructured SiC (n-SiC) are investigated with neutron scattering and molecular-dynamics (MD) techniques. Both MD and the experiment indicate the onset of sintering around 1500 K. During sintering, the pores shrink while maintaining their morphology: the fractal dimension is ∼2 and the surface roughness exponent is ∼0.45. Structural analyses reveal that interfacial regions in n-SiC are disordered with nearly the same number of three- and fourfold coordinated Si atoms. The elastic moduli scale with the density as ∼ρμ, where μ=3.4±0.1.

Scalable I/O of large-scale molecular dynamics simulations: A data-compression algorithm

Disk space, input/output (I/O) speed, and data-transfer bandwidth present a major bottleneck in large-scale molecular dynamics simulations, which require storing positions and velocities of multimillion atoms. A data compression algorithm is designed for scalable I/O of molecular dynamics data. The algorithm uses octree indexing and sorts atoms accordingly on the resulting space-filling curve. By storing differences of successive atomic coordinates and using an adaptive, variable-length encoding to handle exceptional values, the I/O size is reduced by an order-of-magnitude with user-controlled error bound.

Multimillion-atom molecular dynamics simulation of atomic level stresses in Si(111)/Si3N4(0001) nanopixels

Ten million atom multiresolution molecular-dynamics simulations are performed on parallel computers to determine atomic-level stress distributions in a 54 nm nanopixel on a 0.1 µm silicon substrate. Effects of surfaces, edges, and lattice mismatch at the Si(111)/Si3N4(0001) interface on the stress distributions are investigated. Stresses are found to be highly inhomogeneous in the nanopixel. The top surface of silicon nitride has a compressive stress of +3 GPa and the stress is tensile, –1 GPa, in silicon below the interface.

Atomistic simulation of nanostructured materials

Materials and devices with microstructures on the nanometer scale are revolutionizing technology, but until recently simulation at this scale has been problematic. The paper considers how developments in parallel computing are now allowing atomistic simulation using multiresolution algorithms, such as fast multipole methods. With these algorithms, researchers may soon be able to simulate applications up to one billion atoms.The International Conference on Computer Design encompasses technical presentations in all fields of the design and implementation of computer systems and their components. ICCDs strength lies in its multidisciplinary character, covering practical and theoretical issues in systems and computer architecture, verification and testing, design and technology, and tools and methodologies. In contrast to most conferences that are specialized in a certain field, ICCD provides an ideal environment for researchers, developers, and students to receive leading-edge information on a wide range of topics related to their own work.

Large-scale atomistic modeling of nanoelectronic structures

Large-scale molecular-dynamics simulations are performed on parallel computers to study critical issues on ultrathin dielectric films and device reliability in next-decade semiconductor devices. New interatomic-potential models based on many-body, reactive, and quantum-mechanical schemes are used to study various atomic-scale effects: growth of oxide layers; dielectric properties of high-permittivity oxides; dislocation activities at semiconductor/dielectric interfaces; effects of amorphous layers and pixellation on atomic-level stresses in lattice-mismatched nanopixels; and nanoindentation testing of thin films. Enabling technologies for 10 to 100 million-atom simulations of nanoelectronic structures are discussed, which include multiresolution algorithms for molecular dynamics, load balancing, and data management. In ten years, this scalable software infrastructure will enable trillion-atom simulations of realistic device structures with sizes well beyond /spl mu/m on petaflop computers.

Million atom molecular dynamics simulations of materials on parallel computers

Recent advances in computing technology - parallel computer architectures, portable software and development of robust O(N) algorithms - have revolutionized the field of computer simulation. Using ...

Parallel Molecular Dynamics Simulations of High Temperature Ceramics

Abstract ‘Grand Challenge’ atomistic simulations of high-temperature structural materials are performed on multiple, parallel platforms. The simulations focus on sintering of ceramic nanoclusters, structure and mechanical properties of nanophase ceramics, and hypervelocity impact damage in diamond coatings.

Molecular Dynamics Simulations of Nanoindentation of Silicon Nitride

This is a report of work in progress on 10 million atom Molecular Dynamics (MD) simulations of nanoindentation of crystalline and amorphous silicon nitride (Si 3 N 4 ). Nanoindentation is used to determine mechanical properties of extremely thin films such as hardness and elastic moduli. We report load-displacement curves for several Si 3 N 4 configurations using an idealized non-deformable indenter and analyze the local stress distributions in the vicinity of the indenter tip. Preliminary results for surface adhesion using Si 3 N 4 for both tip and substrate are also reported.

Large-scale molecular dynamics study of amorphous carbon and graphite on parallel machines

Using a reactive empirical bond-order potential (REBOP) model for hydrocarbons 1 , large scale molecular dynamics simulations of carbon systems are carried out on parallel machines. Structural and dynamical correlations of amorphous carbon at various densities are studied. The calculated structure factor agrees well with neutron scattering experiments and the results of tightbinding molecular dynamics simulations. The dynamic behavior of crack propagation through graphite sheet is also investigated with the molecular-dynamics method. Effects of external stress and initial notch shape on crack propagation in graphite are studied. It is found that graphite sheet fractures in a cleavage-like or branching manners depending on the orientations of the graphite sheet with respect to the external stress. The roughness of crack surfaces is analyzed. Two roughness exponents are observed in two different regions.

N-body problems: Atomistic simulation of nanostructured materials

Materials and devices with microstructures on the nanometer scale are revolutionizing technology, but until recently simulation at this scale has been problematic. Developments in parallel computing are now allowing atomistic simulation using multiresolution algorithms, such as fast multipole methods. With these algorithms, researchers may soon be able to simulate applications up to one billion atoms.