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

Introduction. Nonlinear Optical Susceptibilities. General Description of Wave Propagation in Nonlinear Media. Electrooptical and Magnetooptical Effects. Optical Rectification and Optical Field-Induced Magnetization. Sum-Frequency Generation. Harmonic Generation. Difference Frequency Generation. Parametric Amplification and Oscillation. Stimulated Raman Scattering. Stimulated Light Scattering. Two-Photon Absorption. High-Resolution Nonlinear Optical Spectroscopy. Four-Wave Mixing. Four-Wave Mixing Spectroscopy. Optical-Field-Induced Birefringence. Self-Focusing. Multiphoton Spectroscopy. Detection of Rare Atoms and Molecules. Laser Manipulation of Particles. Transient Coherent Optical Effects. Strong Interaction of Light with Atoms. Infrared Multiphoton Excitation and Dissociation of Molecules. Laser Isotope Separation. Surface Nonlinear Optics. Nonlinear Optics in Optical Waveguides. Optical Breakdown. Nonlinear Optical Effects in Plasmas. Index.

The Principles of Nonlinear Optics

Optical second-harmonic generation and the related technique of infrared – visible light sum-frequency generation are extremely versatile tools for studies of many kinds of surfaces and interfaces. With the help of ultra-short laser pulses, they can be used to monitor surface dynamics and reactions with sub-picosecond time resolution.

Surface properties probed by second-harmonic and sum-frequency generation

Sum-Frequency Vibrational Spectroscopy on Water Interfaces: Polar Orientation of Water Molecules at Interfaces

Using infrared-visible sum-frequency generation we have obtained the OH stretch vibrational spectra of water at the vapor/water interface. From the spectra, we deduce that more than 20% of the surface water molecules have one free OH projecting into the vapor. The spectrum is weakly temperature dependent from 10 to 80 \ifmmode^\circ\else\textdegree\fi{}C. A monolayer of fatty alcohol on water surface terminates the free OH groups and induces an icelike structure in the spectrum.

Vibrational spectroscopy of water at the vapor/water interface.

Second-order nonlinear optics can be used to quantitatively determine the orientation of chemical bonds or submoieties of a fairly complicated molecule at an interface, and therefore completely map out its orientation and conformation. As a specific example, we have studied pentyl-cyanoterphenyl molecules at the air-water interface. We have measured the orientation of all three parts of the molecule (cyano head group, terphenyl ring, and pentyl chain) by optical second-harmonic generation and infrared-visible sum-frequency generation. A quantitatively consistent picture of the molecular configuration has been obtained. The technique can be applied to situations where other methods would fail (e.g., the surface of neat liquids or buried interfaces).

Y. R. Shen

Papers

The Principles of Nonlinear Optics

Surface properties probed by second-harmonic and sum-frequency generation

Sum-Frequency Vibrational Spectroscopy on Water Interfaces: Polar Orientation of Water Molecules at Interfaces

Vibrational spectroscopy of water at the vapor/water interface.

Mapping molecular orientation and conformation at interfaces by surface nonlinear optics