Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Fast parallel algorithms for short-range molecular dynamics

Geant4 is a software toolkit for the simulation of the passage of particles through matter. It is used by a large number of experiments and projects in a variety of application domains, including high energy physics, astrophysics and space science, medical physics and radiation protection. Over the past several years, major changes have been made to the toolkit in order to accommodate the needs of these user communities, and to efficiently exploit the growth of computing power made available by advances in technology. The adaptation of Geant4 to multithreading, advances in physics, detector modeling and visualization, extensions to the toolkit, including biasing and reverse Monte Carlo, and tools for physics and release validation are discussed here.

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Recent developments in GEANT4

ENDF/B-VII.1 Nuclear Data for Science and Technology: Cross Sections, Covariances, Fission Product Yields and Decay Data

https://digital.library.unt.edu/ark:/67531/metadc888955/m2/1/high_res_d/900147.pdf

ENDF/B-VII.0: Next Generation Evaluated Nuclear Data Library for Nuclear Science and Technology

The fourth version of the Japanese Evaluated Nuclear Data Library has been produced in cooperation with the Japanese Nuclear Data Committee. In the new library, much emphasis is placed on the impro...

https://www.tandfonline.com/doi/pdf/10.1080/18811248.2011.9711675

JENDL-4.0: A New Library for Nuclear Science and Engineering

Evaluation of Neutron Resonance Cross Section Data at GELINA

ORNL Resolved Resonance Covariance Generation for ENDF/B-VII.1

We have analyzed and evaluated {sup 35}Cl, {sup 37}Cl, and {sup nat}Cl neutron cross section data in the resolved resonance region with the multilevel Reich-Moore R-matrix formalism. Energies and widths were determined for 388 resonances in the range 0.2 to 1200 keV. New J assignments were made for 33 resonances, and parities were assigned for 15 of these resonances. Neutron strength functions were calculated for both s and p waves; our results include the first reported p-wave values for Cl. Resonance analyses were carried out with the computer code SAMMY, which utilizes Bayes' method, a generalized least-squares technique. Because SAMMY now has the ability to calculate charged-particle penetrabilities, it was possible to include a proton exit channel in the analysis and to deduce proton widths for several resonances. Our resonance parameter representation describes the data much better than previous evaluations, and it should lead to improved criticality safety calculations for systems where Cl is present.

R-matrix analysis of Cl neutron cross sections up to 1.2 MeV

Neutron capture experiments, using isotopically enriched and natural samples of chromium and titanium, were performed on flight paths 6 and 7 at the 40 m flight station of ORELA. The experimental data were acquired using a pair of deuterated benzene detectors employing the now well-established pulse-height-weighting technique. These data were complemented by new total cross-section measurements where no useful previous data were available.

Neutron Cross-Section Measurements on Structural Materials at ORELA

Many older neutron cross-section evaluations from libraries such as ENDF/B-VI or JENDL-3.2 show deficiencies in energy ranges that are important for criticality safety applications. Consequently, these evaluated data may not be adequate for nuclear criticality calculations where effects such as self-shielding, multiple scattering, or Doppler broadening are important. To support the Nuclear Criticality Safety Program, neutron cross-section measurements have been initiated at the Oak Ridge Electron Linear Accelerator (ORELA). ORELA is ideally suited to measure fission, neutron total, and capture cross-sections in the energy range from 1 eV to ∼600 keV, which is important for many nuclear criticality safety applications.

Klaus H Guber

Papers

Evaluation of Neutron Resonance Cross Section Data at GELINA

ORNL Resolved Resonance Covariance Generation for ENDF/B-VII.1

R-matrix analysis of Cl neutron cross sections up to 1.2 MeV

Neutron Cross-Section Measurements on Structural Materials at ORELA

New neutron cross-section measurements at ORELA and their application in nuclear criticality calculations