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

Metal Oxides and Oxysalts as Anode Materials for Li Ion Batteries

Despite the imminent commercial introduction of Li-ion batteries in electric drive vehicles and their proposed use as enablers of smart grids based on renewable energy technologies, an intensive quest for new electrode materials that bring about improvements in energy density, cycle life, cost, and safety is still underway. This Progress Report highlights the recent developments and the future prospects of the use of phases that react through conversion reactions as both positive and negative electrode materials in Li-ion batteries. By moving beyond classical intercalation reactions, a variety of low cost compounds with gravimetric specific capacities that are two-to-five times larger than those attained with currently used materials, such as graphite and LiCoO(2), can be achieved. Nonetheless, several factors currently handicap the applicability of electrode materials entailing conversion reactions. These factors, together with the scientific breakthroughs that are necessary to fully assess the practicality of this concept, are reviewed in this report.

Beyond Intercalation-Based Li-Ion Batteries: The State of the Art and Challenges of Electrode Materials Reacting Through Conversion Reactions

Recent developments of phosphate glasses for a variety of technological applications, from rare-earth ion hosts for solid state lasers to low temperature sealing glasses, have led to renewed interest in understanding the structures of these unusual materials. In this review, spectroscopic and diffraction studies of simple phosphate glasses, including v-P2O5 and binary phosphate compositions, are described. Special attention is given to the structures of anhydrous ultraphosphate glasses, which have received close attention from the glass community only in the past six years.

Review: the structure of simple phosphate glasses

Sol-gel based materials for biomedical applications

ZnO–B 2 O 3 –P 2 O 5 glasses formulated with Sb 2 O 3 were investigated in the series 50ZnO–10B 2 O 3 –40P 2 O 5  +  x Sb 2 O 3 ( x  = 0–70 mol%). With increasing Sb 2 O 3 content, the values of glass transition temperature decrease from 492 °C down to 394 °C. The dissolution rate of the glasses reveals a maximum for the glass with x  = 15 mol% Sb 2 O 3 . Raman spectra with increasing Sb 2 O 3 content reflect the depolymerisation of phosphate chains. Antimony at low Sb 2 O 3 content forms individual SbO 3 pyramids manifested in the Raman spectra by a broad vibrational band at ∼520–690 cm −1 . In the glasses with a higher Sb 2 O 3 content SbO 3 units link into chains and clusters with Sb–O–Sb bridges manifested in the Raman spectra by a strong broad band at 380–520 cm −1 . The 31 P MAS NMR spectra with increasing Sb 2 O 3 content reflect the depolymerisation of phosphate chains at low Sb 2 O 3 content and only small changes in the PO 4 coordination at a high Sb 2 O 3 content. 11 B MAS NMR spectra reveal a steady transformation of B(OP) 4 units into B(OP) 4− x (OSb) x units, accompanied by the transformation of BO 4 into BO 3 units with increasing Sb 2 O 3 content.

Structure and properties of Sb2O3-containing zinc borophosphate glasses

Conventional quenching methods were used to prepare (50-x/2)Na 2 O.xBi 2 O 3 . (50-x/2) P 2 O 5 system phosphate glasses for x≤16.0. The glass structure was then analysed with infrared and 31 P MAS NMR spectroscopy. The main phosphate species formed by the depolymerisation of the sodium metaphosphate chains by Bi 2 O 3 are firstly chain end groups and then mixed sodium bismuth pyrophosphates. Analysis of the phosphate species shows that some meta and orthophosphates are formed by the equilibrium 2 Q 1 = Q 2 + Q 0 . Infrared and NMR data are in accordance with the covalent character of Bi-O-P bonds. The stereochemically active 6s 2 lone electron pair and the high polarisability of Bi 3+ lead to a highly distorded coordination sphere, with one sided shorter covalent Bi-O bonds and longer ionic Bi-O bonds. The former bonds are the origin of the partial glass forming ability of Bi 3+ .

31P MAS NMR and FT IR analysis of (50−x/2)Na2O.xBi2O3.(50−x/2)P2O5 glasses

http://www.lamav.ufscar.br/artpdf/ssi179.pdf

Increased electrical conductivity of LiPON glasses produced by ammonolysis

This work presents a study on the structure, microstructure and properties of 50Li2O·xB2O3·(50 − x)P2O5 glasses. The structure has been studied through NMR spectroscopy and the microstructure by TEM. The properties of the glasses are discussed according to their structure and microstructural features. The introduction of boron produces new linkages between phosphate chains through P–O–B bonds, whose amount increases with boron incorporation; at the same time, a depolymerisation of the phosphate chains into Q1-type phosphate units takes place. The introduction of boron produces an increase in Tg together with a decrease in the molar volume. The room temperature electrical conductivity increases with boron content as well. However, B2O3 contents higher than 20 mol% lead to crystallisation of lithium orthophosphate which contributed to hinder ionic conduction of the glasses.

Lionel Montagne

Papers

Structure and properties of Sb2O3-containing zinc borophosphate glasses

31P MAS NMR and FT IR analysis of (50−x/2)Na2O.xBi2O3.(50−x/2)P2O5 glasses

Increased electrical conductivity of LiPON glasses produced by ammonolysis

Composition and structure dependence of the properties of lithium borophosphate glasses showing boron anomaly

Combined 17O NMR and 11B-31P double resonance NMR studies of sodium borophosphate glasses.