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

The crystal structures of three β-halolactic acids have been determined, namely, β-chlorolactic acid (systematic name: 3-chloro-2-hydroxypropanoic acid, C3H5ClO3) (I), β-bromolactic acid (systematic name: 3-bromo-2-hydroxypropanoic acid, C3H5BrO3) (II), and β-iodolactic acid (systematic name: 2-hydroxy-3-iodopropanoic acid, C3H5IO3) (III). The number of molecules in the asymmetric unit of each crystal structure (Z') was found to be two for I and II, and one for III, making I and II isostructural and III unique. The difference between the molecules in the asymmetric units of I and II is due to the direction of the hydrogen bond of the alcohol group to a neighboring molecule. Molecular packing shows that each structure has alternating layers of intermolecular hydrogen bonding and halogen-halogen interactions. Hirshfeld surfaces and two-dimensional fingerprint plots were analyzed to further explore the intermolecular interactions of these structures. In I and II, energy minimization is achieved by lowering of the symmetry to adopt two independent molecular conformations in the asymmetric unit.

Crystal structures of three β-halolactic acids: hydrogen bonding resulting in differing Z'.

The new class of contrast enhancement agents can be precisely tuned to aid in vivo photoacoustic tomography.

Improving biomedical imaging with gold nanocages.

As a nanocrystal's structural characteristics relate strongly to its properties, designing increasingly precise syntheses is important for making nanocrystals that are most tailored for a particular application. Importing concepts traditionally associated with the chemistry of small molecules has historically expanded the array of tools available to exert fine control over a nanocrystal's shape and architecture, and consequently its function. Here, we focus on recent work on using concepts from molecular chemistry such as regioselectivity and chemoselectivity in seeded or template-engaged syntheses, and generally draw attention to the idea of having anisotropic, spatially controlled reactivity on a nanocrystal's surface by design.

Sara E. Skrabalak

Papers

Crystal structures of three β-halolactic acids: hydrogen bonding resulting in differing Z'.

Improving biomedical imaging with gold nanocages.

Molecular-like selectivity emerges in nanocrystal chemistry.

Resilient Women and the Resiliency of Science

Inside Cover: Towards Shape Control of Metal Oxide Nanocrystals in Confined Molten Media (ChemNanoMat 1/2015)