Showing papers by "Steven J. Plimpton published in 2000"

Load-balancing techniques for a parallel electromagnetic particle-in-cell code

Abstract: QUICKSILVER is a 3-d electromagnetic particle-in-cell simulation code developed and used at Sandia to model relativistic charged particle transport. It models the time-response of electromagnetic fields and low-density-plasmas in a self-consistent manner: the fields push the plasma particles and the plasma current modifies the fields. Through an LDRD project a new parallel version of QUICKSILVER was created to enable large-scale plasma simulations to be run on massively-parallel distributed-memory supercomputers with thousands of processors, such as the Intel Tflops and DEC CPlant machines at Sandia. The new parallel code implements nearly all the features of the original serial QUICKSILVER and can be run on any platform which supports the message-passing interface (MPI) standard as well as on single-processor workstations. This report describes basic strategies useful for parallelizing and load-balancing particle-in-cell codes, outlines the parallel algorithms used in this implementation, and provides a summary of the modifications made to QUICKSILVER. It also highlights a series of benchmark simulations which have been run with the new code that illustrate its performance and parallel efficiency. These calculations have up to a billion grid cells and particles and were run on thousands of processors. This report also serves as a user manual for people wishing to run parallel QUICKSILVER.

From Atom-Picoseconds to Centimeter-Years in Simulation and Experiment

Abstract: The final report for a Laboratory Directed Research and Development project entitled, ''From Atom-Picoseconds to Centimeter-Years in Simulation and Experiment'' is presented. In this project, separate modeling methods at the atomic scale were used to bridge gaps in time and space with higher scales. For understanding of continuum mechanics quantities at various scales atomistic simulations that ranged from nanometers to microns were performed and experiments from centimeters to millimeters were performed. Certain continuum mechanical quantities were clearly defined as a function of size scale, for example, the yield stress. Several techniques were used to extend the time scale of simulations, including calculating prefactors and activation energies for diffusion events and mapping complex atomic motions onto more tractable lattice models. In the case of transport of small molecules in polymeric and nanoporous materials, new Monte Carlo methods for sampling transition rates were developed.