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

Nanocrystals are fundamental to modern science and technology. Mastery over the shape of a nanocrystal enables control of its properties and enhancement of its usefulness for a given application. Our aim is to present a comprehensive review of current research activities that center on the shape-controlled synthesis of metal nanocrystals. We begin with a brief introduction to nucleation and growth within the context of metal nanocrystal synthesis, followed by a discussion of the possible shapes that a metal nanocrystal might take under different conditions. We then focus on a variety of experimental parameters that have been explored to manipulate the nucleation and growth of metal nanocrystals in solution-phase syntheses in an effort to generate specific shapes. We then elaborate on these approaches by selecting examples in which there is already reasonable understanding for the observed shape control or at least the protocols have proven to be reproducible and controllable. Finally, we highlight a number of applications that have been enabled and/or enhanced by the shape-controlled synthesis of metal nanocrystals. We conclude this article with personal perspectives on the directions toward which future research in this field might take.

Shape‐Controlled Synthesis of Metal Nanocrystals: Simple Chemistry Meets Complex Physics?

Recent years have seen a renewed interest in the harvesting and conversion of solar energy. Among various technologies, the direct conversion of solar to chemical energy using photocatalysts has received significant attention. Although heterogeneous photocatalysts are almost exclusively semiconductors, it has been demonstrated recently that plasmonic nanostructures of noble metals (mainly silver and gold) also show significant promise. Here we review recent progress in using plasmonic metallic nanostructures in the field of photocatalysis. We focus on plasmon-enhanced water splitting on composite photocatalysts containing semiconductor and plasmonic-metal building blocks, and recently reported plasmon-mediated photocatalytic reactions on plasmonic nanostructures of noble metals. We also discuss the areas where major advancements are needed to move the field of plasmon-mediated photocatalysis forward.

Plasmonic-metal nanostructures for efficient conversion of solar to chemical energy

Nanocrystals (NCs) discussed in this Review are tiny crystals of metals, semiconductors, and magnetic material consisting of hundreds to a few thousand atoms each. Their size ranges from 2-3 to about 20 nm. What is special about this size regime that placed NCs among the hottest research topics of the last decades? The quantum mechanical coupling * To whom correspondence should be addressed. E-mail: dvtalapin@uchicago.edu. † The University of Chicago. ‡ Argonne National Lab. Chem. Rev. 2010, 110, 389–458 389

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Prospects of Colloidal Nanocrystals for Electronic and Optoelectronic Applications

Localized Surface Plasmon Resonance Sensors

Au/Pd octopods, nanostructures with eight branches and a primarily Au interior, have been synthesized as size-controlled samples through the manipulation of seed-mediated co-reduction. The position of their localized surface plasmon resonance can be controllably tuned throughout the visible and near-infrared regions, and this response is correlated with the structural features (branch length and tip width) of the octopods. These Au/Pd octopods were also found to be highly sensitive to changes in the local refractive index of the surrounding media and suitable substrates for surface enhanced Raman spectroscopy. These findings, coupled with their unique composition, highlight the multifunctional capabilities of the Au/Pd octopods and provide insight into the optical properties of architecturally controlled bimetallic nanostructures.

Size-controlled synthesis of Au/Pd octopods with high refractive index sensitivity.

A new, mechanically stable silica microparticle with macrosized internal pores (1.6 μm particles with 100 nm pores) has been developed for chromatography. The particles are characterized by an exte...

Sub 2-μm macroporous silica particles derivatized for enhanced lectin affinity enrichment of glycoproteins.

By controlling the kinetics of nanocrystal growth via a galvanic replacement process, branched Au nanocrystals, including Au tetrapods and star-shaped decahedra, have been synthesized in high yield. Such control is achieved by the establishment of a Pt(II)/Pt redox couple during nanocrystal formation, which provides locally high concentrations of Au adatoms via galvanic replacement. These remarkable structures have been extensively characterized by microscopy techniques, which illustrate that the internal twin features of the nanocrystals provide a break in the symmetry of the face centered cubic lattice of the Au particles and account for the specific branching patterns observed. Significantly, this study validates a new class of redox couples for use in nanosyntheses and will enable the preparation of other nanocrystals as kinetic products.

Controlling the Growth Kinetics of Nanocrystals via Galvanic Replacement: Synthesis of Au Tetrapods and Star-Shaped Decahedra

The catalytic and optical properties of metal nanoparticles can be combined to create platforms for light-driven chemical energy storage and enhanced in-situ reaction monitoring. However, the heavily damped plasmon resonances of many catalytically active metals (e.g. Pt, Pd) prevent this dual functionality in pure nanostructures. The addition of catalytic metals at the surface of efficient plasmonic particles thus presents a unique opportunity if the resonances can be conserved after coating. Here, nanometer resolution electron-based techniques (electron energy loss, cathodoluminescence, and energy dispersive X-ray spectroscopy) are used to show that Au particles incorporating a catalytically active but heavily damped metal, Pd, sustain multiple size-dependent localized surface plasmon resonances (LSPRs) that are narrow and strongly localized at the Pd-rich tips. The resonances also couple with a dielectric substrate and other nanoparticles, establishing that the full range of plasmonic behavior is observed in these multifunctional nanostructures despite the presence of Pd.

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Resonances of nanoparticles with poor plasmonic metal tips

Ultrasonic spray pyrolysis has been used as a facile aerosol route to macroporous SiO2 particles using simple inorganic salts as a pore template and colloidal SiO2 as building blocks to the larger porous particles. As we found, the use of template salts with low melting points was vital to macroporous particle synthesis, as a dynamic droplet phase can be maintained throughout product formation. Otherwise, relatively compact particles are produced. Significantly, this approach avoids the need for post-isolation elimination of the template, instead permitting aqueous removal during product collection. Produced particles were characterized by SEM, TEM, and surface area and pore size measurements, while the influence of the selected salts on the reactivity between the building block SiO2 colloids is discussed.

Sara E. Skrabalak

Papers

Size-controlled synthesis of Au/Pd octopods with high refractive index sensitivity.

Sub 2-μm macroporous silica particles derivatized for enhanced lectin affinity enrichment of glycoproteins.

Controlling the Growth Kinetics of Nanocrystals via Galvanic Replacement: Synthesis of Au Tetrapods and Star-Shaped Decahedra

Resonances of nanoparticles with poor plasmonic metal tips

Aerosol synthesis of porous particles using simple salts as a pore template.