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LANL Roadrunner simulates nanoscale material failure
October 30, 2009Very tiny wires, called nanowires, made from such metals as silver and gold, may play a crucial role as electrical or mechanical switches in the development of future-generation ultrasmall nanodevices.
Making nanodevices work will require a deep understanding of how these and other nanostructures can be engineered and fabricated as well as their resultant strengths and weaknesses. How mechanical properties change at the nanoscale is of fundamental interest and may have implications for a variety of nanostructures and nanodevices.
A major limiting factor to this understanding has been that experiments to test how nanowires deform are many times slower than computer simulations can go, resulting in more uncertainty in the simulation predictions than scientists would like.
"Molecular dynamics simulations have been around for a long time," said Arthur Voter of the Theoretical Division at Los Alamos National Laboratory. "But the simulations have never before been able to mimic the atomistic tensile strength of nanowires at time scales that even come close to experimental reality."
Using the "parallel-replica dynamics" method for reaching long time scales that Voter developed, members of Voter's team adapted their computer code to exploit the Roadrunner supercomputer's hybrid architecture, allowing them to perform the first-ever simulation of a stretching silver nanowire over a period of a millisecond, or one-thousandth of a second, a time that approaches what can be tested experimentally.
"Bigger supercomputers have made it possible to perform simulations on larger and larger systems, but they have not helped much with reaching longer times -- the best we can do is still about a millionth of a second. However, with the parallel-replica algorithm, we can utilize the large number of processors to 'parallelize' time," said Voter. "Roadrunner is ideally suited to this algorithm, so now we can do simulations thousands of times longer than this."
With this new tool, scientists can better study what nanowires do under stress. "At longer time scales we see interesting effects. When the wires are stretched more slowly, their behavior changes -- the deformation and failure mechanisms are very different than what we've seen at shorter time scales," said Voter.
Through these simulations, Voter and his team are developing a better understanding of how materials behave when they are reduced to the size scale of a nanometer, or one-billionth of a meter. "At this scale, the motion of just one single atom can change the material's mechanical or electrical properties," said Voter, "so it is really helpful to have a tool that can give us full atomic resolution on realistic time scales, almost as if we are watching every atom as the experiment proceeds."
DOE/Los Alamos National Laboratory
"Molecular dynamics simulations have been around for a long time," said Arthur Voter of the Theoretical Division at Los Alamos National Laboratory. "But the simulations have never before been able to mimic the atomistic tensile strength of nanowires at time scales that even come close to experimental reality."
Using the "parallel-replica dynamics" method for reaching long time scales that Voter developed, members of Voter's team adapted their computer code to exploit the Roadrunner supercomputer's hybrid architecture, allowing them to perform the first-ever simulation of a stretching silver nanowire over a period of a millisecond, or one-thousandth of a second, a time that approaches what can be tested experimentally.
"Bigger supercomputers have made it possible to perform simulations on larger and larger systems, but they have not helped much with reaching longer times -- the best we can do is still about a millionth of a second. However, with the parallel-replica algorithm, we can utilize the large number of processors to 'parallelize' time," said Voter. "Roadrunner is ideally suited to this algorithm, so now we can do simulations thousands of times longer than this."
With this new tool, scientists can better study what nanowires do under stress. "At longer time scales we see interesting effects. When the wires are stretched more slowly, their behavior changes -- the deformation and failure mechanisms are very different than what we've seen at shorter time scales," said Voter.
Through these simulations, Voter and his team are developing a better understanding of how materials behave when they are reduced to the size scale of a nanometer, or one-billionth of a meter. "At this scale, the motion of just one single atom can change the material's mechanical or electrical properties," said Voter, "so it is really helpful to have a tool that can give us full atomic resolution on realistic time scales, almost as if we are watching every atom as the experiment proceeds."
DOE/Los Alamos National Laboratory
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Harvard scientists bend nanowires into 2-D and 3-D structures
Taking nanomaterials to a new level of structural complexity, scientists have determined how to introduce kinks into arrow-straight nanowires, transforming them into zigzagging two- and three-dimensional structures with correspondingly advanced functions.
Putting a Strain on Nanowires Could Yield Colossal Results
In finally answering an elusive scientific question, researchers with the U.S. Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) have shown that the selective placement of strain can alter the electronic phase and its spatial arrangement in correlated electron materials.
Friction force differences could offer a new means for sorting and assembling nanotubes
Nanotubes and nanowires are promising building blocks for future integrated nanoelectronic and photonic circuits, nanosensors, interconnects and electro-mechanical nanodevices. But some fundamental issues remain to be resolved - among them, how to position and manipulate the tiny tubes.
Making more efficient fuel cells
Bacteria that generate significant amounts of electricity could be used in microbial fuel cells to provide power in remote environments or to convert waste to electricity.
Caltech and IBM scientists use self-assembled DNA scaffolding to build tiny circuit boards
Scientists at the California Institute of Technology (Caltech) and IBM's Almaden Research Center have developed a new technique to orient and position self-assembled DNA shapes and patterns-or "DNA origami"-on surfaces that are compatible with today's semiconductor manufacturing equipment.
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