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.

/pdf/self-assembled-monolayers-of-thiolates-on-metals-as-a-form-1neb0hj3k4.pdf

Self-assembled monolayers of thiolates on metals as a form of nanotechnology.

Fundamentals of Plasmonics.- Electromagnetics of Metals.- Surface Plasmon Polaritons at Metal / Insulator Interfaces.- Excitation of Surface Plasmon Polaritons at Planar Interfaces.- Imaging Surface Plasmon Polariton Propagation.- Localized Surface Plasmons.- Electromagnetic Surface Modes at Low Frequencies.- Applications.- Plasmon Waveguides.- Transmission of Radiation Through Apertures and Films.- Enhancement of Emissive Processes and Nonlinearities.- Spectroscopy and Sensing.- Metamaterials and Imaging with Surface Plasmon Polaritons.- Concluding Remarks.

/pdf/plasmonics-fundamentals-and-applications-4syb9877sr.pdf

Plasmonics: Fundamentals and Applications

The interest in nanoscale materials stems from the fact that new properties are acquired at this length scale and, equally important, that these properties * To whom correspondence should be addressed. Phone, 404-8940292; fax, 404-894-0294; e-mail, mostafa.el-sayed@ chemistry.gatech.edu. † Case Western Reserve UniversitysMillis 2258. ‡ Phone, 216-368-5918; fax, 216-368-3006; e-mail, burda@case.edu. § Georgia Institute of Technology. 1025 Chem. Rev. 2005, 105, 1025−1102

Chemistry and properties of nanocrystals of different shapes.

The aggregation kinetics of colloidal silica is highly dependent on conditions such as the {ital p}H and salt concentration. In this paper we investigate the aggregation of colloidal silica under conditions that promote rapid growth, contrasting our findings with earlier investigations of the slow growth of silica. A number of interesting effects are observed, including power-law growth of the mean aggregate radius, dependence of the aggregation rate on concentration and the chemical nature of the salt used, a reduced aggregate fractal dimension, fragmentation of the fast aggregates under changing solution conditions, and shear-induced restructuring of aggregates. Finally, we present evidence that the fractal dimension of aggregates is not strongly universal, but depends weakly on such factors as the solution concentration. We conclude that although the diffusion-limited cluster-cluster aggregation model gives a good first-order description of rapid aggregation, real systems exhibit richer behavior that is not given to such a facile interpretation.

Fast aggregation of colloidal silica

A general constitutive model is presented for calculating the evolution of stresses in crosslinking polymers. The analysis is valid for thermo- and chemorheologically simple polymers and for time-dependent strain histories where the total strain at any time is not large, such that linear viscoelasticity applies. We identify the material parameters required and outline experimental and theoretical methods for their determination. This formalism is then used to calculate the development of cure stresses for an epoxy wherein the glass transition temperature exceeds the cure temperature during the reaction. Finally, we discuss practical methods of stress minimization through control of the cure cycle.

Calculation of Stresses in Crosslinking Polymers

We have used two-dimensional light scattering to study the structure and dynamics of a single-scattering electrorheological fluid in the quiescent state and in steady and oscillatory shear. Studies of the quiescent fluid show that particle columns grow in two stages. Particles first chain along the electric field, causing scattering lobes to appear orthogonal to the field, and then aggregate into columns, causing the scattering lobes to move to smaller angles. Column formation can be understood in terms of a thermal coarsening model we present, whereas the early-time scattering in the direction parallel to the field can be compared to the theory of line liquids. In simple shear the scattering lobes are inclined in the direction of fluid vorticity, in detailed agreement with the independent droplet model of the shear thinning viscosity. In oscillatory shear the orientation of the scattering lobes varies nonsinusoidally. This nonlinear dynamics is described by a kinetic chain model, which provides a theory of the nonlinear shear rheology in arbitrary shear flows. {copyright} {ital 1998} {ital The American Physical Society}

Structure and dynamics of electrorheological fluids

We have investigated the mechanism of nano-YAG:Ce growth in butanediol and glycol solvents. The static autoclave and low synthesis temperature (225 °C) that we employed provided conditions of slow growth in which we were able to observe an intermediate phase, a butanediol-intercalated layered alumina. This phase serves to passivate the surface in nano-YAG:Ce precipitates and thus contributes to increasing the quantum yield of YAG:Ce by diminishing surface effects such as Ce oxidation. While neat 1,4-butanediol results in precipitation of the nano-YAG:Ce, a mixture of 1,4-butanediol and diethylene glycol stabilizes a transparent colloid. We attribute this to higher solubility of the layered alumina intermediate in the solvent mixture and, thus, more homogeneous nucleation of the nano-YAG:Ce compared to heterogeneous nucleation in the neat 1,4-butanediol. However, the trade-off is slightly lower quantum yield in the transparent colloid, since the nano-YAG:Ce is not as thoroughly surface-passivated. With the...

Nano-YAG:Ce Mechanisms of Growth and Epoxy-Encapsulation

Silica/surfactant mesophases have been synthesized in 14 water:cosolvent mixtures by combining tetramethoxysilane with a basic 2 wt % CTAB solution. The effects of the water-to-cosolvent ratio on t...

James E. Martin

Papers

Fast aggregation of colloidal silica

Calculation of Stresses in Crosslinking Polymers

Structure and dynamics of electrorheological fluids

Nano-YAG:Ce Mechanisms of Growth and Epoxy-Encapsulation

Surfactant-templated silica mesophases formed in water:cosolvent mixtures