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

As properties of nanocrystals are size- and shape-dependent, synthetic routes that provide fine control over these structural parameters are required. Traditional solid-state reactions often yield a variety of crystallite morphologies and sizes due to limited control over precursor distribution. In ultrasonic spray synthesis, particle formation occurs within spatially and temporally confined droplets, and, as we show, nanoplates of ilmenite NaSbO3 can be prepared by salt-assisted aerosol combustion. The NaSbO3 nanoplates were used as topotactic templates to synthesize AgSbO3 visible-light photocatalysts. The absolute conduction and valence band positions of AgSbO3 nanoplates were deduced by UV–photoelectron spectroscopy and UV–visible diffuse reflectance spectroscopy. A comparative analysis of model photocatalytic reactions revealed that the surface chemistry and particle morphology were influential in the photocatalytic activity. Significantly, the integration of combustion chemistry and molten fluxes in...

Aerosol-Assisted Combustion Synthesis of Single-Crystalline NaSbO3 Nanoplates: A Topotactic Template for Ilmenite AgSbO3

Spray synthesis is a robust route to compositionally complex materials as fine powders; however, the solid-state synthetic conditions in most cases limit access to discrete nanoparticles with defined structural features. Yet, by maintaining a dynamic droplet phase through integration of molten salt chemistry, product formation can proceed in manners similar to lower temperature solution routes to nanomaterials. This Focus Review connects concepts from classical nucleation theory and molten salt chemistry to provide a framework for nanocrystal formation via aerosol-assisted molten salt synthesis (AMSS). Examples of metal oxide nanocrystal formation by AMSS are surveyed and highlight how the spatial and temporal confinement of aerosol droplets limits crystal growth in molten media. Ultimately, we strive to provide practical guidelines, not limited to AMSS, towards the synthesis of compositionally complex materials as shape-defined nanocrystals.

Towards Shape Control of Metal Oxide Nanocrystals in Confined Molten Media

In situ liquid cell scanning transmission electron microscopy probes seeded growth in real time. The growth of Pd on Au nanocubes is monitored as a model system to compare growth within a liquid cell and traditional colloidal synthesis. Different growth patterns are observed due to seed immobilization and the highly reducing environment within the liquid cell.

Impact of Membrane-Induced Particle Immobilization on Seeded Growth Monitored by In Situ Liquid Scanning Transmission Electron Microscopy.

Stellated bimetallic nanostructures are a new class of plasmonic colloids in which the interplay between composition and overall architecture can provide tunable optical properties and new functionality. However, decoupling the complex compositional and structural contributions to the localized surface plasmon resonance (LSPR) remains a challenge, especially when the monometallic counterparts are not synthetically accessible for comparison. Here, stellated Au–Pd nanocrystals (NCs) with Oh symmetry are used as a model system to decouple structural and complex compositional effects on LSPR. Single-particle correlation of the LSPR with the structure of octopodal Au–Pd NCs was achieved using optical dark-field spectroscopy with scanning electron microscopy. These measurements were compared to calculations of the optical properties of structurally similar Au-only octopods by the finite difference time domain method. This comparison enabled the role of complex composition, which was determined by scanning trans...

Structure versus Composition: A Single-Particle Investigation of Plasmonic Bimetallic Nanocrystals

Pt-based catalysts are common in fuel cells but suffer from high cost and poor durability. To overcome these limitations, earth-abundant metals are often incorporated with Pt in core@shell architectures or through alloy formation. Here, the concepts of a core@shell architecture, alloyed surfaces, and high-durability intermetallics are integrated into one nanostructure platform using seed-mediated co-reduction (SMCR). Specifically, random alloy PtM (where M = Ni, Co, Cu, or Fe) shells are deposited on intermetallic PdCu B2 seeds. Control of shell thickness and Pt:M ratios is also demonstrated, providing a general route to strain-engineered alloyed surfaces. The performance of these nanocatalysts was evaluated for the oxygen reduction reaction (ORR) as a function of shell thickness and shell composition, where PtCu and PtNi shells showed a 230% and 270% activity increase, respectively, compared to the Pt reference. This evaluation is coupled with Tafel plot analysis which shows significant changes in the Ta...

Sara E. Skrabalak

Papers

Aerosol-Assisted Combustion Synthesis of Single-Crystalline NaSbO3 Nanoplates: A Topotactic Template for Ilmenite AgSbO3

Towards Shape Control of Metal Oxide Nanocrystals in Confined Molten Media

Impact of Membrane-Induced Particle Immobilization on Seeded Growth Monitored by In Situ Liquid Scanning Transmission Electron Microscopy.

Structure versus Composition: A Single-Particle Investigation of Plasmonic Bimetallic Nanocrystals

Building Random Alloy Surfaces from IntermetallicSeeds: A General Route to Strain-Engineered Electrocatalysts with High Durability