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Simulation and modeling of the electronic structure of GaAs damage clusters

Journal of Applied Physics

Moussa, Jonathan E.; Foiles, Stephen M.; Schultz, Peter A.

In an effort to build a stronger microscopic foundation for radiation damage models in gallium arsenide (GaAs), the electronic properties of radiation-induced damage clusters are studied with atomistic simulations. Molecular dynamics simulations are used to access the time and length scales required for direct simulation of a collision cascade, and density functional theory simulations are used to calculate the electronic properties of isolated damaged clusters that are extracted from these cascades. To study the physical properties of clusters, we analyze the statistics of a randomly generated ensemble of damage clusters because no single cluster adequately represents this class of defects. The electronic properties of damage clusters are accurately described by a classical model of the electrical charging of a semiconducting sphere embedded in a uniform dielectric. The effective band gap of the cluster depends on the degree of internal structural damage, and the gap closes to form a metal in the high-damage limit. We estimate the Fermi level of this metallic state, which corresponds to high-energy amorphous GaAs, to be 0.46 ± 0.07 eV above the valence band edge of crystalline GaAs. © 2013 American Institute of Physics.

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TYPE Journal Article YEAR 2013
OSTIScopus

Data co-processing for extreme scale analysis level II ASC milestone (4745)

Rogers, David R.; Moreland, Kenneth D.; Oldfield, Ron A.; Fabian, Nathan D.

Exascale supercomputing will embody many revolutionary changes in the hardware and software of high-performance computing. A particularly pressing issue is gaining insight into the science behind the exascale computations. Power and I/O speed con- straints will fundamentally change current visualization and analysis work ows. A traditional post-processing work ow involves storing simulation results to disk and later retrieving them for visualization and data analysis. However, at exascale, scien- tists and analysts will need a range of options for moving data to persistent storage, as the current o ine or post-processing pipelines will not be able to capture the data necessary for data analysis of these extreme scale simulations. This Milestone explores two alternate work ows, characterized as in situ and in transit, and compares them. We nd each to have its own merits and faults, and we provide information to help pick the best option for a particular use.

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TYPE SAND Report YEAR 2013
DOIOSTI

Penetration of rod projectiles in semi-infinite targets : a validation test for Eulerian X-FEM in ALEGRA

Niederhaus, John H.; Park, Byoung P.

The finite-element shock hydrodynamics code ALEGRA has recently been upgraded to include an X-FEM implementation in 2D for simulating impact, sliding, and release between materials in the Eulerian frame. For validation testing purposes, the problem of long-rod penetration in semi-infinite targets is considered in this report, at velocities of 500 to 3000 m/s. We describe testing simulations done using ALEGRA with and without the X-FEM capability, in order to verify its adequacy by showing X-FEM recovers the good results found with the standard ALEGRA formulation. The X-FEM results for depth of penetration differ from previously measured experimental data by less than 2%, and from the standard formulation results by less than 1%. They converge monotonically under mesh refinement at first order. Sensitivities to domain size and rear boundary condition are investigated and shown to be small. Aside from some simulation stability issues, X-FEM is found to produce good results for this classical impact and penetration problem.

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TYPE SAND Report YEAR 2013
DOIOSTI
Results 6726–6750 of 9,998
Results 6726–6750 of 9,998