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

Atomic vapors have played an important role in recent work on optical mixing. They have been used to generate tunable IR radiation, tunable vacuum UV, and coherent radiation with wavelengths as short as 380 A. Until recently, the schemes used all involved susceptibilities derived by keeping only the dipole interaction of light with the medium. Recently we reported second order sum-frequency generation in Na vapor.[1] The dipole susceptibility for second order mixing vanishes for a vapor, and a more general type of susceptibility must be considered to describe this process.[2] For example, our Na sum-frequency generation can be described as phase matched emission from oscillating atomic quadrupole moments driven at frequency ω3 = ωl + ω2 by two applied fields, as shown schematically in Fig. 1. The quadrupole moment density is given by: 

$$\begin{gathered} \underline{\underline Q} = {\underline{\underline X} ^{(Q)}}:{\underline E _1}{\underline E _2} \hfill \\ {\text{ = }}{{\text{X}}^{(Q)}}{\text{ }}[{\underline E _1}{\underline E _2} + {\underline E _2}{\underline E _1} - \frac{2}{3}\underline{\underline I} ({\underline E _1} \cdot {\underline E _2})]. \hfill \\ \end{gathered} $$

(1)

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Second-order sum- and difference-frequency generation via quadrupole transitions in atomic vapors

Summary form only given. Surface vibrational spectroscopy via infrared-visible sum-frequency generation (SFG) has been developed into a powerful tool to study structures of surfaces and interfaces. With various input/output polarization combinations, the SFG vibrational spectra can yield detailed information about orientational distributions of selected atomic groups at a surface or interface. However, in all quantitative SFG studies reported so far, the dynamic nature of molecules have been ignored. In some cases, this practice has resulted in difficulty to understand the observed spectra. In this paper we show that the effect of rotational or librational motion of molecules on their vibrational spectra can be significant.

Effect of molecular motion on surface vibrational spectra

Analysis of the spinning motion of liquid crystal molecules is reported for the first time. A femtosecond pump probe Kerr effect experiment allowed us to evidence both individual and collective contributions to this motion.

Femtosecond Analysis of the Spinning Motion of Liquid Crystal Molecules in Smectic A Phases

Raman-streuung durch nematische, fluessig-kristalline 4,4′-bis-(alkoxy)-azoxybenzole

Sum-frequency vibrational spectroscopy (SFVS) and second-harmonic generation (SHG) were used to probe the structures of rubbed surfaces of polyimide (PI) with and without side chains and the alignment of liquid crystal (LC) monolayers adsorbed on them. The SFVS spectra show clearly the presence of rubbing-induced anisotropy indicating the induced alignment of the PI backbones at the surface, but they hardly exhibit any rubbing-induced anisotropy. The results lead to the conclusion that while the PI backbones are aligned by rubbing, the orientation of alkyl side chains are hardy affected because they are projecting out normally from the surface with a broad orientational distribution. The SHG measurement indicates that the LC monolayers adsorbed on the polymer are more or less aligned along the rubbing direction. The order parameter of the LC monolayer on the rubbed PI with alkyl side chains is smaller than that on the PI without alkyl side chains.

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Y. R. Shen

Papers

Second-order sum- and difference-frequency generation via quadrupole transitions in atomic vapors

Effect of molecular motion on surface vibrational spectra

Femtosecond Analysis of the Spinning Motion of Liquid Crystal Molecules in Smectic A Phases

Raman-streuung durch nematische, fluessig-kristalline 4,4′-bis-(alkoxy)-azoxybenzole

Nonlinear Optical Spectroscopic Studies of Polyimide Surfaces and LC Adsorbates