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

Bull. Chem. Soc. Jpn. への投稿のすすめ

The use of light to mediate controlled radical polymerization has emerged as a powerful strategy for rational polymer synthesis and advanced materials fabrication. This review provides a comprehensive survey of photocontrolled, living radical polymerizations (photo-CRPs). From the perspective of mechanism, all known photo-CRPs are divided into either (1) intramolecular photochemical processes or (2) photoredox processes. Within these mechanistic regimes, a large number of methods are summarized and further classified into subcategories based on the specific reagents, catalysts, etc., involved. To provide a clear understanding of each subcategory, reaction mechanisms are discussed. In addition, applications of photo-CRP reported so far, which include surface fabrication, particle preparation, photoresponsive gel design, and continuous flow technology, are summarized. We hope this review will not only provide informative knowledge to researchers in this field but also stimulate new ideas and applications to further advance photocontrolled reactions.

http://pubs.acs.org/doi/pdf/10.1021/acs.chemrev.5b00671

Light-Controlled Radical Polymerization: Mechanisms, Methods, and Applications

Metal-mediated and metal-catalyzed reactions of isocyanides.

Photoactivation of Ruthenium Olefin Metathesis Initiators

Olefin metathesis catalysed by ruthenium has emerged at the frontier of modern synthetic chemistry. The desire to enhance catalyst stability, gain control over the catalytic process and deepen the understanding of the mechanisms of metathesis has yielded a class of latent ruthenium precatalysts of delayed initiation and with switchable activity. One of the main methodologies developed for this purpose has been the introduction of tethered carbene ligands. Herein we track the evolution of ruthenium based metathesis catalysts bearing chelated alkylidenes, from the early oxygen Hoveyda type benzylidenes to the latent sulphur containing complexes.

Chelating alkylidene ligands as pacifiers for ruthenium catalysed olefin metathesis

Light activation is a most desirable property for catalysis control. Among the many catalytic processes that may be activated by light, olefin metathesis stands out as both academically motivating and practically useful. Starting from early tungsten heterogeneous photoinitiated metathesis, up to modern ruthenium methods based on complex photoisomerisation or indirect photoactivation, this survey of the relevant literature summarises past and present developments in the use of light to expedite olefin ring-closing, ring-opening polymerisation and cross-metathesis reactions.

https://www.beilstein-journals.org/bjoc/content/pdf/1860-5397-6-127.pdf

Light-induced olefin metathesis

Widening the Latency Gap in Chelated Ruthenium Olefin Metathesis Catalysts

Olefin metathesis has greatly impacted polymer, organic, and organometallic chemistry during the last decades. Thus, the development of well-defined metathesis catalysts and the search to expand the substrate range under various conditions is a highly active area of research. Ruthenium olefin metathesis catalysts (Fig. 1) are of special interest as a result of their higher stability and leniency towards various functional groups. Olefin metathesis reactions may be classified into three main categories. Ring-closing metathesis (RCM) is characterized by an intermolecular reaction between catalyst and substrate followed by an intramolecular reaction, resulting in product formation and regeneration of the active catalytic species. Cross metathesis (CM) or acyclic diene metathesis polymerization (ADMET) proceeds by two subsequent bimolecular steps, also releasing the active catalyst to the solution. On the other hand, in ring-opening metathesis polymerization (ROMP), the initiator reacts with a monomer and remains attached to the product until termination (decomposition). ROMP and ADMET have shown many important industrial applications, consequently, the study and development of new methods in metatheses polymerizations is a valued objective. Although stability and activity are fundamental factors when thinking about any catalysis, precise mechanistic control is certainly a central concern in polymer production, since the physical properties of the product are strongly dependent on polymer size, polydispersity, and tacticity. In typical ROMP reactions, following the initial exchange of the benzylidene with a monomer, the produced propagating species is virtually equivalent for catalysts 2, 3, and 4 (Scheme 1). The disparities between these kind of catalysts, therefore, should only be interpreted as a consequence of initiation rate differences. An important distinction in the case of bidentate chelated catalysts is that the substituted styrene may return to the 14-electron active catalytic form via CM, regenerating the precatalytic 16-electron species with a longer half-life; this is known as the ‘‘boomerang effect.’’ However, in ROMP, chelation has a lesspronounced effect on stability (the propagating species is more stable due to the absence of methylidene complexes), and furthermore, it has been shown to impose a negative effect on polydispersity. Recently, we developed highly stable sulfur-chelated ruthenium complexes that display latency at room temperature, and determined that their activities at higher temperatures could be modulated as a function of steric acceleration factors. As dormancy in polymerization reactions is a sought asset, we decided to study whether this appealing characteristic is maintained in Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 47, 4209–4213 (2009)

https://www.onlinelibrary.wiley.com/doi/pdf/10.1002/pola.23476

Yuval Vidavsky

Papers

Photoactivation of Ruthenium Olefin Metathesis Initiators

Chelating alkylidene ligands as pacifiers for ruthenium catalysed olefin metathesis

Light-induced olefin metathesis

Widening the Latency Gap in Chelated Ruthenium Olefin Metathesis Catalysts

A latent s-chelated ruthenium benzylidene initiator for ring-opening metathesis polymerization