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

Although gold is the subject of one of the most ancient themes of investigation in science, its renaissance now leads to an exponentially increasing number of publications, especially in the context of emerging nanoscience and nanotechnology with nanoparticles and self-assembled monolayers (SAMs). We will limit the present review to gold nanoparticles (AuNPs), also called gold colloids. AuNPs are the most stable metal nanoparticles, and they present fascinating aspects such as their assembly of multiple types involving materials science, the behavior of the individual particles, size-related electronic, magnetic and optical properties (quantum size effect), and their applications to catalysis and biology. Their promises are in these fields as well as in the bottom-up approach of nanotechnology, and they will be key materials and building block in the 21st century. Whereas the extraction of gold started in the 5th millennium B.C. near Varna (Bulgaria) and reached 10 tons per year in Egypt around 1200-1300 B.C. when the marvelous statue of Touthankamon was constructed, it is probable that “soluble” gold appeared around the 5th or 4th century B.C. in Egypt and China. In antiquity, materials were used in an ecological sense for both aesthetic and curative purposes. Colloidal gold was used to make ruby glass 293 Chem. Rev. 2004, 104, 293−346

Gold nanoparticles: assembly, supramolecular chemistry, quantum-size-related properties, and applications toward biology, catalysis, and nanotechnology.

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Self-assembled monolayers of thiolates on metals as a form of nanotechnology.

Fundamentals of Plasmonics.- Electromagnetics of Metals.- Surface Plasmon Polaritons at Metal / Insulator Interfaces.- Excitation of Surface Plasmon Polaritons at Planar Interfaces.- Imaging Surface Plasmon Polariton Propagation.- Localized Surface Plasmons.- Electromagnetic Surface Modes at Low Frequencies.- Applications.- Plasmon Waveguides.- Transmission of Radiation Through Apertures and Films.- Enhancement of Emissive Processes and Nonlinearities.- Spectroscopy and Sensing.- Metamaterials and Imaging with Surface Plasmon Polaritons.- Concluding Remarks.

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Plasmonics: Fundamentals and Applications

The interest in nanoscale materials stems from the fact that new properties are acquired at this length scale and, equally important, that these properties * To whom correspondence should be addressed. Phone, 404-8940292; fax, 404-894-0294; e-mail, mostafa.el-sayed@ chemistry.gatech.edu. † Case Western Reserve UniversitysMillis 2258. ‡ Phone, 216-368-5918; fax, 216-368-3006; e-mail, burda@case.edu. § Georgia Institute of Technology. 1025 Chem. Rev. 2005, 105, 1025−1102

Chemistry and properties of nanocrystals of different shapes.

The mechanisms of temperature-dependent nonradiative processes, often referred to as thermal quenching, are studied in CdSe, CdSe/ZnSe, and CdTe nanoparticles. These particles exhibit reversible thermal quenching, the extent of which is strongly dependent on the composition of the surface and nature of the surface ligands. Thermal quenching has dynamic (affecting the luminescence lifetimes) and static (affecting the fraction of particles that are bright versus dark) components. The temperature dependence of quantum yields and time-resolved luminescence decays as well as room temperature transient absorption spectroscopy are used to elucidate the thermal quenching mechanisms. Dynamic thermal quenching is due to thermally activated trapping dynamics that occur on the same time scale as the radiative lifetime. This paper focuses on static thermal quenching and several different mechanisms are considered. It is concluded that the dominant mechanism involves thermal promotion of valence band electrons to empty...

Thermal quenching mechanisms in II-VI semiconductor nanocrystals

Electrorheology of a model colloidal fluid

Synthesis of highly magnetic iron nanoparticles suitable for field structuring using a β-diketone surfactant

A series of dilute tetramethoxysilicon gels was made in order to study the spatial correlations that arise from the presence of solvent. Light-scattering measurements from these gels show a fractal structure on length scales as large as 1 \ensuremath{\mu}m. The short-length-scale fractal dimension differs from that observed for the connectivity transition at the gel point, indicating a crossover in universality class. Quasielastic light scattering measurements on the incipient gel demonstrate a critical slowing down in the relaxation of concentration fluctuations, causing frozen inhomogeneities in the final gels. Finally, the growth at early times, where the clusters are smaller than the spatial correlation length of the final gel, is shown to be exponential in time, in accord with models of aggregation. It is concluded that a kinetic model of gelation is needed to describe the short-length-scale structures observed in these gels.

Spatial correlations and growth in dilute gels

Dynamic light-scattering measurements on fractal aggregates of colloidal silica show that the mean decay rate (Rayleigh linewidth) of the intensity autocorrelation function scales like q/sup 2.7/, where q is the momentum transfer. This result is compared to the q/sup 3/ prediction for percolation clusters and the more complex results derived here for cluster-cluster aggregation.

James E. Martin

Papers

Thermal quenching mechanisms in II-VI semiconductor nanocrystals

Electrorheology of a model colloidal fluid

Synthesis of highly magnetic iron nanoparticles suitable for field structuring using a β-diketone surfactant

Spatial correlations and growth in dilute gels

Dynamics of fractal colloidal aggregates