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

The lithium metal battery is strongly considered to be one of the most promising candidates for high-energy-density energy storage devices in our modern and technology-based society. However, uncontrollable lithium dendrite growth induces poor cycling efficiency and severe safety concerns, dragging lithium metal batteries out of practical applications. This review presents a comprehensive overview of the lithium metal anode and its dendritic lithium growth. First, the working principles and technical challenges of a lithium metal anode are underscored. Specific attention is paid to the mechanistic understandings and quantitative models for solid electrolyte interphase (SEI) formation, lithium dendrite nucleation, and growth. On the basis of previous theoretical understanding and analysis, recently proposed strategies to suppress dendrite growth of lithium metal anode and some other metal anodes are reviewed. A section dedicated to the potential of full-cell lithium metal batteries for practical applicatio...

Toward Safe Lithium Metal Anode in Rechargeable Batteries: A Review.

This review covers important advances in recent years in the physics of thin-film ferroelectric oxides, the strongest emphasis being on those aspects particular to ferroelectrics in thin-film form. The authors introduce the current state of development in the application of ferroelectric thin films for electronic devices and discuss the physics relevant for the performance and failure of these devices. Following this the review covers the enormous progress that has been made in the first-principles computational approach to understanding ferroelectrics. The authors then discuss in detail the important role that strain plays in determining the properties of epitaxial thin ferroelectric films. Finally, this review ends with a look at the emerging possibilities for nanoscale ferroelectrics, with particular emphasis on ferroelectrics in nonconventional nanoscale geometries.

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Physics of thin-film ferroelectric oxides

Thermoelectrics have long been recognized as a potentially transformative energy conversion technology due to their ability to convert heat directly into electricity. Despite this potential, thermoelectric devices are not in common use because of their low efficiency, and today they are only used in niche markets where reliability and simplicity are more important than performance. However, the ability to create nanostructured thermoelectric materials has led to remarkable progress in enhancing thermoelectric properties, making it plausible that thermoelectrics could start being used in new settings in the near future. Of the various types of nanostructured materials, bulk nanostructured materials have shown the most promise for commercial use because, unlike many other nanostructured materials, they can be fabricated in large quantities and in a form that is compatible with existing thermoelectric device configurations. The first generation of these materials is currently being developed for commercialization, but creating the second generation will require a fundamental understanding of carrier transport in these complex materials which is presently lacking. In this review we introduce the principles and present status of bulk nanostructured materials, then describe some of the unanswered questions about carrier transport and how current research is addressing these questions. Finally, we discuss several research directions which could lead to the next generation of bulk nanostructured materials.

Bulk nanostructured thermoelectric materials: current research and future prospects

The conversion efficiency of heat to electricity in thermoelectric materials depends on both their thermopower and electrical conductivity. It is now reported that, unlike their inorganic counterparts, organic thermoelectric materials show an improvement in both these parameters when the volume of dopant elements is minimized; furthermore, a high conversion efficiency is achieved in PEDOT:PSS blends.

Engineered doping of organic semiconductors for enhanced thermoelectric efficiency

We report results on the activation field and frequency dependence of the coercive voltage in epitaxial ferroelectric thin film capacitors. Frequency dependent hysteresis loops and pulse width dependent polarization of epitaxial La0.5Sr0.5CoO3/(Pb,La)(Zr,Ti)O3/La0.5Sr0.5CoO3 capacitor structures were measured as a function of La content. The coercive voltages and their frequency dependence vary systematically with increasing La content. We show that the activation field for polarization reversal is directly related to the c/a ratio (tetragonality ratio) of the ferroelectric layer. A larger c/a ratio leads to a larger field to activate the motion of domain walls through the lattice. An important consequence of a larger activation field is a stronger pulse width dependence of the pulse switched polarization.

Activation field of ferroelectric (Pb,La)(Zr,Ti)O3 thin film capacitors

Shrinking feature size and increasing transistor density, combined with the high performance demanded from next-generation microprocessors, have led to on-chip high heat flux “hot spots,” which have emerged as the primary driver for thermal management of today's integrated circuit (IC) technology. This article describes the use of a mini-contact to enhance the cooling flux of a miniaturized thermoelectric cooler (TEC) for on-chip hot-spot remediation. A package-level numerical simulation is developed to predict the on-chip hot spot cooling capability achievable with such a mini-contact enhanced TEC. Attention is focused on the hot-spot temperature reduction associated with variations in mini-contact size and thermoelectric element height, as well as the parasitic effect from the thermal contact resistance introduced by the mini-contact. A preliminary experiment has been conducted to verify the numeric model and to demonstrate the effects of the mini-contact on hot-spot cooling.

Mini-Contact Enhanced Thermoelectric Coolers for On-Chip Hot Spot Cooling

A combination of factors—notably environmental concerns about global warming and ozone depletion due to refrigerants and the increasing demand for electronics and optoelectronic cooling—led to renewed activity in alternative cooling technologies. Currently, thermoelectric cooling is considered a popular cooling technology. This paper provides a critical review of thermoelectric technology and assesses its potential applications in air conditioning and refrigeration. The first part of this paper is devoted to the basic concept of thermoelectrics, with an overview of current thermoelectric materials and devices. The second part is a general overview of the applications of thermoelectric technology, with an emphasis on those related to air conditioning and refrigeration.

Review Article: Thermoelectric Technology Assessment: Application to Air Conditioning and Refrigeration

Cellulose nanofiber (CNF) from abundant and renewable wood is an emerging material with excellent mechanical, chemical, and optical properties. Transparent nanopaper made of CNF (CNF-nanopaper) could potentially replace plastics in electronics due to its excellent optical transparency, mechanical strength, and biodegradability. However, CNF-nanopaper normally has a low thermal conductivity and poor stability in increasing temperatures, which is not suitable for long-term stability and reliability in devices. Herein, for the first time, we report a thermally conductive, electrically insulating, and optically transparent nanopaper using a bilayer design where a thin layer of boron nitride (BN) nanosheets were coated on the CNF-nanopaper. An optical transparency (70%) and a thermal conductivity (0.76 W/m/K) were successfully achieved through a solution-based process at room temperature. Such an optically transparent, electrically insulating, and thermally conductive bilayer nanopaper can find applications in...

Bao Yang

Papers

Activation field of ferroelectric (Pb,La)(Zr,Ti)O3 thin film capacitors

Mini-Contact Enhanced Thermoelectric Coolers for On-Chip Hot Spot Cooling

Review Article: Thermoelectric Technology Assessment: Application to Air Conditioning and Refrigeration

Thermally Conductive, Electrical Insulating, Optically Transparent Bi-Layer Nanopaper.

Textile Electronics for VR/AR Applications