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

High refractive index sensitivity (RIS) of branched Au-Pd nanocrystals (NCs) is engineered through lowering the dielectric dispersion at the NC resonant wavelength with internal or external atomic % Pd. To our knowledge, these NCs display the highest ensemble RIS measurement for colloids with LSPR maximum band positions ≤900 nm, and these results are corroborated with FDTD computations.

Engineering high refractive index sensitivity through the internal and external composition of bimetallic nanocrystals

Different materials and the capabilities they enabled have marked the ages of civilization. For example, the malleable copper alloys of the Bronze Age provided harder and more durable tools. Most exploration of new alloys has focused on random alloys, in which the alloying metal sites have no metal preference. In binary and ternary metal systems, dissimilar elements do not mix readily at high concentrations, which has limited alloying studies to intermetallics (ordered multimetallic phases) and random alloys, in which minor components are added to a principal element. In 2004, crystalline metal alloys consisting of five or more principal elements in equal or nearly equal amounts ( 1 , 2 ) were reported that were stabilized by their high configurational entropy. Unlike most random alloys, the “high-entropy” alloys ( 3 , 4 ) reside in the centers of their multidimensional phase diagrams (see the figure, right). On page 1489 of this issue, Yao et al. ( 5 ) present an innovative and general route to high-entropy alloys that can mix up to eight elements into single-phase, size-controlled nanoparticles (NPs).

https://science.sciencemag.org/content/sci/359/6383/1467.full.pdf

Mashing up metals with carbothermal shock

Manipulating the architecture of Pd@Pt nanostructures through metal-selective capping agent interactions

Nanostructures with well-defined crystallite sizes, shapes, and compositions are finding use in areas such as energy, security, and even medicine. Seeded growth is a promising strategy to achieve shape-controlled nanostructures, where specific structural features are often directed by the underlying symmetry of the seeds. Here, thiophenol derivatives capable of different metal-thiolate interactions were introduced into the synthesis of Au/Pd nanostructures by seed-mediated co-reduction. Our systematic analysis reveals that the symmetry and composition of the bimetallic nanoparticles (NPs) can be tuned as a function of additive binding strength and concentration, with symmetry reduction observed in some cases. Furthermore, additives with both thiol and amine functionalities facilitate random branching on the octahedral seed. Significantly, this synthetic versatility arises because the thiophenol derivatives modify both the surface capping of the growing nanostructures and the local ligand environment of the metal precursors, highlighting how the dual roles of synthesis components can be exploited to achieve high quality bimetallic nanostructures.

Sara E. Skrabalak

Papers

Engineering high refractive index sensitivity through the internal and external composition of bimetallic nanocrystals

Mashing up metals with carbothermal shock

Manipulating the architecture of Pd@Pt nanostructures through metal-selective capping agent interactions

Surface versus solution chemistry: manipulating nanoparticle shape and composition through metal–thiolate interactions

Designer Plasmonic Nanostructures for Unclonable Anticounterfeit Tags