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

Energy density is the main property of rechargeable batteries that has driven the entire technology forward in past decades. Lithium-ion batteries (LIBs) now surpass other, previously competitive battery types (for example, lead–acid and nickel metal hydride) but still require extensive further improvement to, in particular, extend the operation hours of mobile IT devices and the driving mileages of all-electric vehicles. In this Review, we present a critical overview of a wide range of post-LIB materials and systems that could have a pivotal role in meeting such demands. We divide battery systems into two categories: near-term and long-term technologies. To provide a realistic and balanced perspective, we describe the operating principles and remaining issues of each post-LIB technology, and also evaluate these materials under commercial cell configurations. Post-lithium-ion batteries are reviewed with a focus on their operating principles, advantages and the challenges that they face. The volumetric energy density of each battery is examined using a commercial pouch-cell configuration to evaluate its practical significance and identify appropriate research directions.

Promise and reality of post-lithium-ion batteries with high energy densities

Leu-M

ZnO nanostructures for optoelectronics: Material properties and device applications

Small Angle Scattering of X-Rays

Carbon-coated high capacity layered Li[Li0.2Mn0.54Ni0.13Co0.13]O2 cathodes

In this work, we synthesized ZnO nanorods by a wet chemical process. By varying different parameters of the synthesis process like precursor concentration, solvent used, surfactant, temperature, and reaction time, we were able to control the aspect ratio (l/d) and sharpness factor (Sf = h/b) of the rods. Rods with an aspect ratio of ∼20 and a sharpness factor of 10 were repeatedly obtained and characterized from scanning electron microscopy. High-resolution transmission electron microscopy and dark field analysis revealed that nanorods grow as a single crystal along the c axis [0001]. UV and visible emission was obtained in both flat- and sharp-terminated rods. According to the XPS analysis, rods present an excess of Zn2+ of ∼4% that is responsible for the strong yellow emission band. Such defects were removed by annealing of the sample at 200 °C for 2 h. Possible mechanisms of changes in the morphology produced by changes in the synthesis process are also discussed.

Controlling the growth and luminescence properties of well-faceted ZnO nanorods

The electrode films fabricated with the high capacity layered oxide Li[Li0.2Mn0.54Ni0.13Co0.13]O2 have been surface modified with metallic aluminum by a thermal evaporation process. The morphology and electrochemical performances of the bare and the Al-coated cathodes have been investigated by scanning electron microscopy (SEM) and charge−discharge measurements. Compared to the bare Li[Li0.2Mn0.54Ni0.13Co0.13]O2 cathode, the Al-coated cathodes (coating time ≤ 30 s) exhibit higher discharge capacity with lower irreversible capacity loss, better cyclability, and higher rate capability. Specifically, the 20 s Al-coated cathode exhibits the highest capacity (278 mAh/g at C/20 rate) and the best rate capability (157 mAh/g at 5C rate), while the 30 s Al-coated cathode displays the best cyclability (268 mAh/g with a capacity retention of 98% in 50 cycles). An analysis of the charge−discharge capacity values, surface conductivity evaluation, and electrochemical impedance spectroscopy (EIS) measurements reveal tha...

Conductive Surface Modification with Aluminum of High Capacity Layered Li[Li0.2Mn0.54Ni0.13Co0.13]O2 Cathodes

Synthesis of assembled ZnO structures by precipitation method in aqueous media

Thin films find a variety of technological applications. Assembling thin films from atoms in the liquid phase is intrinsically a non-equilibrium phenomenon, controlled by the competition between thermodynamics and kinetics. We demonstrate here that microwave energy can assist in assembling atoms into thin films directly on a substrate at significantly lower temperatures than conventional processes, potentially enabling plastic-based electronics. Both experimental and electromagnetic simulation results show microwave fields can selectively interact with a conducting layer on the substrate despite the discrepancy between the substrate size and the microwave wavelength. The microwave interaction leads to localized energy absorption, heating, and subsequent nucleation and growth of the desired films. Electromagnetic simulations show remarkable agreement with experiments and are employed to understand the physics of the microwave interaction and identify conditions to improve uniformity of the films. The films can be patterned and grown on various substrates, enabling their use in widespread applications.

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B. Reeja-Jayan

Papers

Carbon-coated high capacity layered Li[Li0.2Mn0.54Ni0.13Co0.13]O2 cathodes

Controlling the growth and luminescence properties of well-faceted ZnO nanorods

Conductive Surface Modification with Aluminum of High Capacity Layered Li[Li0.2Mn0.54Ni0.13Co0.13]O2 Cathodes

Synthesis of assembled ZnO structures by precipitation method in aqueous media

Microwave-assisted Low-temperature Growth of Thin Films in Solution