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

Since the discovery of mechanically exfoliated graphene in 2004, research on ultrathin two-dimensional (2D) nanomaterials has grown exponentially in the fields of condensed matter physics, material science, chemistry, and nanotechnology. Highlighting their compelling physical, chemical, electronic, and optical properties, as well as their various potential applications, in this Review, we summarize the state-of-art progress on the ultrathin 2D nanomaterials with a particular emphasis on their recent advances. First, we introduce the unique advances on ultrathin 2D nanomaterials, followed by the description of their composition and crystal structures. The assortments of their synthetic methods are then summarized, including insights on their advantages and limitations, alongside some recommendations on suitable characterization techniques. We also discuss in detail the utilization of these ultrathin 2D nanomaterials for wide ranges of potential applications among the electronics/optoelectronics, electrocat...

Recent Advances in Ultrathin Two-Dimensional Nanomaterials

Metal species with different size (single atoms, nanoclusters, and nanoparticles) show different catalytic behavior for various heterogeneous catalytic reactions. It has been shown in the literature that many factors including the particle size, shape, chemical composition, metal–support interaction, and metal–reactant/solvent interaction can have significant influences on the catalytic properties of metal catalysts. The recent developments of well-controlled synthesis methodologies and advanced characterization tools allow one to correlate the relationships at the molecular level. In this Review, the electronic and geometric structures of single atoms, nanoclusters, and nanoparticles will be discussed. Furthermore, we will summarize the catalytic applications of single atoms, nanoclusters, and nanoparticles for different types of reactions, including CO oxidation, selective oxidation, selective hydrogenation, organic reactions, electrocatalytic, and photocatalytic reactions. We will compare the results o...

Metal Catalysts for Heterogeneous Catalysis: From Single Atoms to Nanoclusters and Nanoparticles.

Single-atom catalysis has arguably become the most active new frontier in heterogeneous catalysis. Aided by recent advances in practical synthetic methodologies, characterization techniques and computational modelling, we now have a large number of single-atom catalysts (SACs) that exhibit distinctive performances for a wide variety of chemical reactions. This Perspective summarizes recent experimental and computational efforts aimed at understanding the bonding in SACs and how this relates to catalytic performance. The examples described here illustrate the utility of SACs in a broad scope of industrially important reactions and highlight the advantages these catalysts have over those presently used. SACs have well-defined active centres, such that unique opportunities exist for the rational design of new catalysts with high activities, selectivities and stabilities. Indeed, given a certain practical application, we can often design a suitable SAC; thus, the field has developed very rapidly and afforded promising catalyst leads. Moreover, the control we have over certain SAC structures paves the way for designing base metal catalysts with the activities of noble metal catalysts. It appears that we are entering a new era of heterogeneous catalysis in which we have control over well-dispersed single-atom active sites whose properties we can readily tune. Single-atom catalysts are heterogeneous materials featuring active metals sites atomically dispersed on a surface. This Review describes methods by which we prepare and characterize these materials, as well as how we can tune their catalytic performance in a variety of important reactions.

Heterogeneous single-atom catalysis

A new strategy for achieving stable Co single atoms (SAs) on nitrogen-doped porous carbon with high metal loading over 4 wt % is reported. The strategy is based on a pyrolysis process of predesigned bimetallic Zn/Co metal–organic frameworks, during which Co can be reduced by carbonization of the organic linker and Zn is selectively evaporated away at high temperatures above 800 °C. The spherical aberration correction electron microscopy and extended X-ray absorption fine structure measurements both confirm the atomic dispersion of Co atoms stabilized by as-generated N-doped porous carbon. Surprisingly, the obtained Co-Nx single sites exhibit superior ORR performance with a half-wave potential (0.881 V) that is more positive than commercial Pt/C (0.811 V) and most reported non-precious metal catalysts. Durability tests revealed that the Co single atoms exhibit outstanding chemical stability during electrocatalysis and thermal stability that resists sintering at 900 °C. Our findings open up a new routine for general and practical synthesis of a variety of materials bearing single atoms, which could facilitate new discoveries at the atomic scale in condensed materials.

Single Cobalt Atoms with Precise N-Coordination as Superior Oxygen Reduction Reaction Catalysts

We have studied the multiple recording method to estimate if it possible to obtain by this way reliable EXAFS data standard deviations. The examination of more than 10 different samples, each of them recorded at least 8 times, gave us the possibility to show that the partial standard deviations follow the expected probability laws. Even when the number of samples is small, it is possible to give a reasonable upper limit of e wich could be used as the statistical contribution of the experimental error bars. In some cases we have found that a uniform weighting by 1/e 2 may fail to give a good fit, especially in the high part of k space. We present a simple method of weighting which lead to more satisfying fits without loosing the correct normalisation of the fitted AX 2 necessary to obtain correct fitted parameters error bars.

Estimation of the experimental standard deviations in EXAFS measurements

EXAFS Data Analysis of Vitamin B12 Model Compounds − A Methodological Study

CeO2-based redox nanomaterials are widely used in automotive catalysts, solid oxide fuel cell systems and many other applications as highly efficient redox systems. However, these properties suffer thermal deactivation under real operating conditions and accordingly thermal stability is a highly desirable property. We report that highly dispersed and intimately intermixed CeO2–ZrO2–BaO–Al2O3 nanocomposites can be synthesized by direct one-pot synthesis. With an appropriate choice of dopant concentration, a self-assembly mechanism is triggered on calcination at high temperatures to form a network of inter-grown stabilized transition aluminas and CexZr1−xO2 nanocrystals anchored over barium hexaaluminate which show remarkable catalytic properties and an excellent stability against thermal and redox ageing.

Self-assembly of one-pot synthesized CexZr1−xO2–BaO·nAl2O3 nanocomposites promoted by site-selective doping of alumina with barium

Stepwise construction of silica-supported tantalum/iridium heteropolymetallic catalysts using surface organometallic chemistry

Photocatalysis and photoelectrochemical (PEC) activities not only strongly depend on the chemical formulae of the electrode materials, but also on the local ionic environment that deserves to be ad...

Emiliano Fonda

Papers

Estimation of the experimental standard deviations in EXAFS measurements

EXAFS Data Analysis of Vitamin B12 Model Compounds − A Methodological Study

Self-assembly of one-pot synthesized CexZr1−xO2–BaO·nAl2O3 nanocomposites promoted by site-selective doping of alumina with barium

Stepwise construction of silica-supported tantalum/iridium heteropolymetallic catalysts using surface organometallic chemistry

Epitaxial TiO2 Thin Film Photoanodes: Influence of Crystallographic Structure and Substrate Nature