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

Using optical second-harmonic generation, we have studied the orientational order of cyanobiphenyl liquid-crystal monolayers at the interface between a mica crystal and a liquid-crystal film put in the presence of ethylene glycol vapor. These small, volatile molecules adsorb at the mica surface and significantly affect the orientational order of the surface liquid-crystal molecules. As the chemical potential of the volatile molecules was increased, this orientational order first varied continuously, and at a certain stage, exhibited a discontinuous change corresponding to a first-order orientational transition. This surface transition drives the first-order anchoring transition (i.e., the reorientation of the bulk liquid crystal) previously observed in these systems.

Anchoring of nematic liquid crystals on mica in the presence of volatile molecules.

We show that second-order coherent sum-frequency generation via quadrupole transitions in metal vapors can be easily detected. The process is as strong as the allowed third-order processes. Our experimental results agree very well with theoretical predictions. (AIP)

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Optical Quadrupole Sum-Frequency Generation in Sodium Vapor

Sum frequency vibrational spectroscopy was used to study adsorption of leucine molecules at air-water interface from solutions with different concentrations and pH values The surface density and the orientation of the isopropyl head group of the adsorbed leucine molecules could be deduced from the measurements It was found that the orientation depends on the surface density, but only weakly on bulk pH value at the saturated surface density The vibrational spectra of the interfacial water molecules appeared to be strongly affected by the charge state of the adsorbed leucine molecules Enhancement and inversion of polar orientation of interfacial water molecules by surface charges or field controllable by the bulk pH value were observed

Sum frequency vibrational spectroscopy of leucine molecules adsorbed at air-water interface.

Chiral sum-frequency (SF) spectroscopy that measures both the real and the imaginary components of the SF spectral response was demonstrated for the first time. It was based on interference of the SF signal with a dispersionless SF reference. Solutions of 1,1‘-bi-2-naphthol (BN) were used as model systems, and their chiral SF spectra over the first exciton-split transitions were obtained. Chiral spectra are useful for determination of absolute configuration and conformation of chiral molecules.

Toward chiral sum-frequency spectroscopy.

A simple theory is given to explain the many different features of small-scale filaments under various experimental conditions. It is shown that the observed filaments are the consequences of moving foci. Under appropriate conditions, a focal spot can move in the forward direction with a speed faster than light. As a result, the light pulse emitted from the filament at the end of the nonlinear medium has a much shorter duration than the input pulse, and shows a characteristic spectral broadening. Because of its high intensity, a moving focal spot also leaves behind it a temporary track of field-induced refractive index. Light trailing after the focal spot can then be partially trapped in the track. Trapping over an appreciable distance is possible if the velocity of the forward-moving focal spot is not much higher than the light velocity.

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Y. R. Shen

Papers

Anchoring of nematic liquid crystals on mica in the presence of volatile molecules.

Optical Quadrupole Sum-Frequency Generation in Sodium Vapor

Sum frequency vibrational spectroscopy of leucine molecules adsorbed at air-water interface.

Toward chiral sum-frequency spectroscopy.

Theoretical Interpretation of Small-Scale Filaments of Light Originating from Moving Focal Spots