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

Brillouin scattering is used to study the propagation of hypersonicwaves in a cholesteric medium at the liquid-to-liquid-crystal tramition. Contrary to the results obtained by others, we have found no anomalouschange in either the velocity or the attenuation of the hypersonic waves at the transition.

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Brillouin Scattering in a Cholesteric Liquid Crystal Near the Cholesteric-Isotropic Transition

https://escholarship.org/content/qt9hx4j92h/qt9hx4j92h.pdf?t=p2au7d

Self-focusing: From transient to quasi-steady-state

Picosecond laser pulses were used to study the highly forbidden resonant second-harmonic generation (SHG) in potassium vapor. The input intensity dependence, vapor density dependence, buffer-gas pressure dependence, and spatial profile of the SHG were measured. A pump–probe experiment was conducted to probe the time dependence of the SHG signal. The experimental results can be understood from an ionization-initiated dc-field-induced SHG model. A theory of a dc-field-induced SHG model is developed that takes into account the time development of the dc electric field in detail. This temporal buildup of the dc field along with transient coherent excitation between two-photon-allowed transitions can explain the experimental results quantitatively, including the previous vapor SHG results with nanosecond laser pulses.

Second-harmonic generation in atomic vapor with picosecond laser pulses

The total amount of the adsorbed polystyrene with a zwitterionic (SO 3 − (CH 2 ) 3 N + Me 2 (CH 2 ) 2 ) end-group. From toluene solutions on hydrophilic glass was measured. It was found that the adsorbed amount is almost independent of molecular weight, in agreement with previous mica force measurements

End-functionalized polymer adsorption study by evanescent ellipsometry

Cholesteryl-l-glutamate (CLG) thin films were investigated when deposited on pure water and on saturated solutions of water soluble amino acids, to test the capacity of the CLG monolayer to recognize and incorporate amino acids from the subphase. Analysis of grazing incidence X-ray diffraction measurements indicates that the hydrophobic amino acids, leucine, isoleucine, and valine, are adsorbed between the glutamate moieties, within the CLG crystalline monolayer, but also around their domains, forming, for l-Leu and d-Val, crystalline bilayers. The presence of Cu2+ ions in the aqueous subphase enhances the crystallinity of the CLG monolayer without overly affecting the lateral packing, by bridging glutamate moieties on neighbor molecules. When amino acids are injected in a Cu2+ containing solution, the domain size of the mixed monolayers formed with the CLG molecules and hydrophobic amino acids is drastically increased.

Y. R. Shen

Papers

Brillouin Scattering in a Cholesteric Liquid Crystal Near the Cholesteric-Isotropic Transition

Self-focusing: From transient to quasi-steady-state

Second-harmonic generation in atomic vapor with picosecond laser pulses

End-functionalized polymer adsorption study by evanescent ellipsometry

A crystalline Langmuir monolayer designed as a template for selective intercalation of water soluble α-amino acids