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.

The optical properties of metal nanoparticles have long been of interest in physical chemistry, starting with Faraday's investigations of colloidal gold in the middle 1800s. More recently, new lithographic techniques as well as improvements to classical wet chemistry methods have made it possible to synthesize noble metal nanoparticles with a wide range of sizes, shapes, and dielectric environments. In this feature article, we describe recent progress in the theory of nanoparticle optical properties, particularly methods for solving Maxwell's equations for light scattering from particles of arbitrary shape in a complex environment. Included is a description of the qualitative features of dipole and quadrupole plasmon resonances for spherical particles; a discussion of analytical and numerical methods for calculating extinction and scattering cross-sections, local fields, and other optical properties for nonspherical particles; and a survey of applications to problems of recent interest involving triangula...

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The Optical Properties of Metal Nanoparticles: The Influence of Size, Shape, and Dielectric Environment

The surface science of titanium dioxide

The richness of optical and electronic properties of graphene attracts enormous interest. Graphene has high mobility and optical transparency, in addition to flexibility, robustness and environmental stability. So far, the main focus has been on fundamental physics and electronic devices. However, we believe its true potential lies in photonics and optoelectronics, where the combination of its unique optical and electronic properties can be fully exploited, even in the absence of a bandgap, and the linear dispersion of the Dirac electrons enables ultrawideband tunability. The rise of graphene in photonics and optoelectronics is shown by several recent results, ranging from solar cells and light-emitting devices to touch screens, photodetectors and ultrafast lasers. Here we review the state-of-the-art in this emerging field.

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Graphene photonics and optoelectronics

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Transient Self-Focusing in a Nematic Liquid Crystal in the Isotropic Phase

Y.R. Shen Solitons are solitary waves, sometimes seen in water canals or as light pulses in optical fibers, that propagate for long distances without changing shape. This phenomenon is the result of a delicate balancing act between the tendency for waves to disperse and the nonlinear properties of the propagation medium. As a result of this interaction, the mathematical description of solitons can be highly complex. In his Perspective, Shen discusses a report in the same issue by
 Snyder and Mitchell
 that shows a much simpler way to mathematically approach solitons.

Solitons Made Simple

Correlation between thermal desorption spectroscopy and optical second harmonic generation for monitoring surface coverages

Optical second-harmonic generation has been used to study the effect of coadsorbed small volatile molecules on the orientational order of a liquid crystal monolayer at the interface between a mica surface and a liquid crystal film. As the chemical potential of the volatile molecules was increased, a first-order orientational transition was observed in the monolayer. This surface transition is shown to drive the reorientation of the bulk liquid crystal previously observed in these systems.

Bulk reorientation driven by orientational transition in a liquid crystal monolayer.

Using surface optical second-harmonic generation, we have determined the molecular tilt angle and the in-plane orientational order of the liquid-crystal molecules 4'-n-octyl-4-cyanobiphenyl (8CB) on a series of polyimide surfaces. The polyimides differ in the length of the flexible spacers in between neighboring aromatic cores. Using birefringence measurements, we obtained the bulk tilt angle of liquid-crystal cells having the same series of surfaces. The surface molecular tilt angle, the in-plane orientational ordering near the surface, and the bulk tilt angle all exhibit an odd-even effect related to the odd or even number of spacer units in the polyimides

Y. R. Shen

Papers

Transient Self-Focusing in a Nematic Liquid Crystal in the Isotropic Phase

Solitons Made Simple

Correlation between thermal desorption spectroscopy and optical second harmonic generation for monitoring surface coverages

Bulk reorientation driven by orientational transition in a liquid crystal monolayer.

Correlation between surface and bulk orientations of liquid crystals on rubbed polymer surfaces : odd-even effects of polymer spacer units