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

Deposits of clastic carbonate-dominated (calciclastic) sedimentary slope systems in the rock record have been identified mostly as linearly-consistent carbonate apron deposits, even though most ancient clastic carbonate slope deposits fit the submarine fan systems better. Calciclastic submarine fans are consequently rarely described and are poorly understood. Subsequently, very little is known especially in mud-dominated calciclastic submarine fan systems. Presented in this study are a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) that reveals a >250 m thick calciturbidite complex deposited in a calciclastic submarine fan setting. Seven facies are recognised from core and thin section characterisation and are grouped into three carbonate turbidite sequences. They include: 1) Calciturbidites, comprising mostly of highto low-density, wavy-laminated bioclast-rich facies; 2) low-density densite mudstones which are characterised by planar laminated and unlaminated muddominated facies; and 3) Calcidebrites which are muddy or hyper-concentrated debrisflow deposits occurring as poorly-sorted, chaotic, mud-supported floatstones. These

Phd by thesis

J. Appl. Cryst.の発刊に際して

Diamond-like carbon (DLC) is a metastable form of amorphous carbon with significant sp3 bonding. DLC is a semiconductor with a high mechanical hardness, chemical inertness, and optical transparency. This review will describe the deposition methods, deposition mechanisms, characterisation methods, electronic structure, gap states, defects, doping, luminescence, field emission, mechanical properties and some applications of DLCs. The films have widespread applications as protective coatings in areas, such as magnetic storage disks, optical windows and micro-electromechanical devices (MEMs).

/pdf/diamond-like-amorphous-carbon-3pczopr0z7.pdf

Diamond-like amorphous carbon

Mechanical properties of nanocrystalline materials

Clusters and cluster-assembled materials : Symposium : Meeting : Papers

The amorphous(a)-to-crystalline (c) phase transition has been studied in electron(e ) and/or ion irradiated silicon (Si). The irradiations were performed in situ in the Argonne High Voltage Microscope-Tandem Facility. The irradiation of Si, at <10K, with 1-MeV e to a fluence of 14 dpa failed to induce the c-to-a transition. Whereas an irradiation, at <10K, with 1.0 or 1.5-MeV Kr+ ions induced the c-to-a transition by a fluence of approx.0.37 dpa. Alternatively a dual irradiation, at 10K, with 1.0-MeV e and 1.0 or 1.5-MeV Kr+ to a Kr+ fluence of 1.5 dpa - where the ratio of the displacement rates for e to ions was approx.0.5 - resulted in the Si specimen retaining a degree of crystallinity. These results are discussed in terms of the degree of dispersion of point defects in the primary state of damage and the mobilities of point defects.

/pdf/crystalline-to-amorphous-phase-transition-in-irradiated-404trokhce.pdf

Crystalline-to-amorphous phase transition in irradiated silicon

By using classical molecular dynamics technique we have simulated the effects of 5 keV Xe atoms impinging on the strained Ge(1 0 0) 2×1 surface. We found that large adatom islands are formed on top of the amorphous zones created by the cascades. We also found that lattice atoms around the molten zone move radially inwards and thus cause strain relief in the sample.

Strain effects in Ge surface cascades

Stable index‐guided operation of variable stripe strained‐layer InGaAs‐GaAs‐AlGaAs lasers achieved by MeV oxygen implantation‐induced disorder of the active region is demonstrated. Well‐behaved near‐ and far‐field patterns for lasers implanted with 5×1016 cm−2 and 1×1017 cm−2 oxygen are observed to be stable with increasing drive current. Comparison with unimplanted, oxide‐defined stripe lasers fabricated from the same wafer indicates a dramatic improvement in emission characteristics as a result of the presence of a lateral real‐index waveguide in the oxygen‐disordered regions which is stronger than the carrier‐induced antiguide present in unimplanted InGaAs‐GaAs strained‐layer lasers.

Robert S Averback

Papers

Clusters and cluster-assembled materials : Symposium : Meeting : Papers

Crystalline-to-amorphous phase transition in irradiated silicon

Strain effects in Ge surface cascades

Index‐guided operation in narrow stripe InGaAs‐GaAs strained‐layer quantum well heterostructure lasers by MeV oxygen implantation

The formation of vacancy-type defect clusters by ion bombardment: A problem revisited by molecular dynamics