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 extremely high thermal conductivities of carbon nanotubes have motivated a wealth of research. Progress includes innovative conduction metrology based on microfabricated platforms and scanning thermal probes as well as simulations exploring phonon dispersion and scattering using both transport theory and molecular dynamics. This article highlights these advancements as part of a detailed review of heat conduction research on both individual carbon nanotubes and nanostructured films consisting of arrays of nanotubes or disordered nanotube mats. Nanotube length, diameter, and chirality strongly influence the thermal conductivities of individual nanotubes and the transition from primarily diffusive to ballistic heat transport with decreasing temperature. A key experimental challenge, for both individual nanotubes and aligned films, is the separation of intrinsic and contact resistances. Molecular dynamics simulations have studied the impacts of specific types of imperfections on the nanotube conductance and its variation with length and chirality. While the properties of aligned films fall short of predictions based on individual nanotube data, improvements in surface engagement and postfabrication nanotube quality are promising for a variety of applications including mechanically compliant thermal contacts.

http://nanoheat.stanford.edu/sites/default/files/publications/RevModPhys%20Marconnet%20et%20al..pdf

Thermal conduction phenomena in carbon nanotubes and related nanostructured materials

Advances in the synthesis and scalable manufacturing of single-walled carbon nanotubes (SWCNTs) remain critical to realizing many important commercial applications. Here we review recent breakthroughs in the synthesis of SWCNTs and highlight key ongoing research areas and challenges. A few key applications that capitalize on the properties of SWCNTs are also reviewed with respect to the recent synthesis breakthroughs and ways in which synthesis science can enable advances in these applications. While the primary focus of this review is on the science framework of SWCNT growth, we draw connections to mechanisms underlying the synthesis of other 1D and 2D materials such as boron nitride nanotubes and graphene.

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Carbon Nanotubes and Related Nanomaterials: Critical Advances and Challenges for Synthesis toward Mainstream Commercial Applications

Polymers are usually considered thermal insulators, because the amorphous arrangement of the molecular chains reduces the mean free path of heat-conducting phonons. The most common method to increase thermal conductivity is to draw polymeric fibres, which increases chain alignment and crystallinity, but creates a material that currently has limited thermal applications. Here we show that pure polythiophene nanofibres can have a thermal conductivity up to ∼ 4.4 W m(-1) K(-1) (more than 20 times higher than the bulk polymer value) while remaining amorphous. This enhancement results from significant molecular chain orientation along the fibre axis that is obtained during electropolymerization using nanoscale templates. Thermal conductivity data suggest that, unlike in drawn crystalline fibres, in our fibres the dominant phonon-scattering process at room temperature is still related to structural disorder. Using vertically aligned arrays of nanofibres, we demonstrate effective heat transfer at critical contacts in electronic devices operating under high-power conditions at 200 °C over numerous cycles.

High thermal conductivity of chain-oriented amorphous polythiophene

Sub-micrometer-sized colloidal graphite (CG) was tested as a conducting electrode to replace transparent conducting oxide (TCO) electrodes and as a catalytic material to replace platinum (Pt) for I...

Sub-micrometer-sized Graphite As a Conducting and Catalytic Counter Electrode for Dye-sensitized Solar Cells

Experimental characterization of dynamic heat exchanger behavior

Characterization of Metallically Bonded Carbon Nanotube-Based Thermal Interface Materials Using a High Accuracy 1D

Carbon Nanotube Arrays for Enhanced Thermal Interfaces to Thermoelectric Modules

Thermal interface materials (TIMs) serve a critical role in the thermal management of electronic systems by enhancing the flow of heat from source to sink Nanostructured materials, such as arrays of carbon nanotubes (CNTs) have been shown to outperform many commercially available TIMs due to their low intrinsic resistance and large compliance that enables them to conform to rough surfaces These characteristics, combined with their low density and ability to withstand vacuum environments and extreme temperatures, make CNT-based TIMs very suitable for space applications In space, materials are exposed to high doses of gamma radiation due to the lack of an atmosphere to serve as an absorbing medium With typical design lifetimes of 5 to 10 years or even more, total radiation exposure can be significant and can affect the structure and performance of the TIM In this work, the potentially adverse effects on the thermal performance of CNT TIMs of gamma-ray irradiation is reported CNT TIMs were irradiated in a gamma cell at a rate of 250 rad/s to total doses of 50 and 100 Mrad The thermal interface resistance was measured before and after gamma-ray irradiation using a transient photoacoustic (PA) method at room temperature and a contact pressure of 134 kPa and indicated no adverse effects of gamma-ray exposure on thermal performanceCopyright © 2013 by ASME

Effect of Gamma-Ray Irradiation on the Thermal Contact Conductance of Carbon Nanotube Thermal Interface Materials

Carbon nanotube (CNT) arrays are attractive thermal interface materials with high compliance and conductance that can remain effective over a wide temperature range. Here we study CNT interface structures in which free CNT ends are bonded using palladium hexadecanethiolate Pd(SC16 H35 )2 to an opposing substrate (one-sided interface) or opposing CNT array (two-sided interface) to enhance contact conductance while maintaining a compliant joint. The palladium weld is particularly attractive for its mechanical stability at high temperatures. A transient photoacoustic (PA) method is used to measure the thermal resistance of the palladium bonded CNT interfaces. The interfaces were bonded at moderate pressures and then tested at 34 kPa using the PA technique. At an interface temperature of approximately 250°C, one-sided and two-sided palladium bonded interfaces achieved thermal resistances near 10 mm2 K/W and 5 mm2 K/W, respectively.Copyright © 2009 by ASME

Stephen L. Hodson

Papers

Experimental characterization of dynamic heat exchanger behavior

Characterization of Metallically Bonded Carbon Nanotube-Based Thermal Interface Materials Using a High Accuracy 1D

Carbon Nanotube Arrays for Enhanced Thermal Interfaces to Thermoelectric Modules

Effect of Gamma-Ray Irradiation on the Thermal Contact Conductance of Carbon Nanotube Thermal Interface Materials

Palladium Thiolate Bonding of Carbon Nanotube Thermal Interfaces for High-Temperature Electronics