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

The surface vibrational spectrum of atactic polypropylene was measured using IR+Visible Sum Frequency Generation (SFG) vibrational spectroscopy, in the temperature range 23 to -50 °C. A sharp rise in the intensity of the C-H symmetric stretch of CH2 groups is observed in the temperature range 0 to -20 °C. The elastic modulus and friction of the same polymer were measured with Atomic Force Microscopy (AFM) in the same temperature range i.e. 23 to -50 °C. There is a sharp rise in the modulus and a sharp decrease in the friction coefficient, at temperatures between 23 and 0 °C. These changes are attributed to the glass transition in atactic polypropylene which is expected to occur in the temperature range 10 to -10 °C. The temperature at which the glass transition is observed, from changes detected in AFM experiments, is higher than that observed by SFG experiments and that expected from bulk measurements. This elevation in the glass transition temperature has been attributed to the high pressure applied to the polymer under the AFM tip.

Correlation of Structure and Mechanical Properties of Polyolefin Surfaces by Ir + Visible Sum Frequency Generation Vibrational Spectroscopy and Atomic Force Microscopy

A variety of metamaterials has been demonstrated recently that support backward waves and negative refraction (Negative Index Materials, NIM.) In particular, these materials enable sub-wavelength r ...

Properties of nanostructured metamaterials at optical frequencies

A transient optical Kerr measurement is used to study molecular reorientation about the long molecular axis of chiral and nonchiral smectic-A liquid crystals. Two relaxation components were identified, associated with individual and collective molecular motions. In contradiction with a recent report [J. R. Lalanne et al., Phys. Rev. Lett. 62, 3046 (1989); Phys. Rev. A 44, 6632 (1991)], no critical behavior of this reorientation was observed as the transition to the ferroelectric smectic-C * phase was approached

Reorientation dynamics of ferroelectric liquid-crystal molecules near the smectic- A -smectic-C* transition

The recent status of applications of nonlinear optics to surface science is reviewed. The basic theory of wave mixing on a surface layer, and the possibility of using various nonlinear optical processes for surface probing are briefly discussed. Emphasis is on surface second harmonic generation, which is shown with many illustrations to be a rather unique and versatile tool for surface studies.

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Nonlinear Optics And Surface Science

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Y. R. Shen

Papers

Correlation of Structure and Mechanical Properties of Polyolefin Surfaces by Ir + Visible Sum Frequency Generation Vibrational Spectroscopy and Atomic Force Microscopy

Properties of nanostructured metamaterials at optical frequencies

Reorientation dynamics of ferroelectric liquid-crystal molecules near the smectic- A -smectic-C* transition

Nonlinear Optics And Surface Science

Optical Metamaterials at Near IR Range Fabricated by Nanoimprint Lithography