The invited talk by Eliot Fang was delivered to members of the Materials Research Society at its recent semiannual general meeting.
Sandia is a National Nuclear Security Administration laboratory.
Fang derided the pejorative "garbage in, garbage out" description of computer modeling - the belief that inputs for computer simulations are so generic that outcomes fail to generate the unexpected details found only by actual experiment.
Fang not only denied this truism but reversed it. "There's another, prettier world beyond what the SEM [scanning electron microscope] shows, and it's called simulation," he told his audience. "When you look through a microscope, you don't see some things that modeling and simulation show."
This change in the position of simulations in science - from weak sister to an ace card - is a natural outcome of improvements in computing, Fang says. "Fifteen years ago, the Cray YMP [supercomputer] was the crown jewel; it's now equivalent to a PDA we have in our pocket."
No one denies that experiments are as important as simulations - "equal partners, in fact," says Julia Phillips, director of Sandia's Physical, Chemical, and Nanosciences Center.
But the Labs' current abilities to run simulations with thousands, millions, and even billions of atoms have led to insights that would otherwise not have occurred, Fang says.
For example, one simulation demonstrated that a tiny but significant amount of material had transferred onto the tip of an atomic force microscope (AFM) as it examined the surface of a microsystem.
"The probe tip changed something very, very tiny on the surface of the material," says Fang. "It was almost not noticeable. But the property of the surface became very different."
Laboratory observation couldn't identify the cause of the property change, but computer simulations provided a reasonable explanation of the results.
As for predicting the reliability of materials that coat surfaces, Fang says, "We find that when we compare our simulation models with data from the experiments, we get a more complete understanding."
Says Sandia Fellow and materials researcher Jeff Brinker, "We use simulations quite a bit in support of Sandia's water purification program and the NIH Nano-Medicine Center program. In all these cases I'm working with theorists and modelers to guide the design of synthetic nanopores so as to develop transport behaviors approaching those of natural water or ion channels that exist in cell membranes."
How is this understanding achieved?
Models computationally link a variety of size and time scales to create an experimental design.
"We use as much experimental information as possible to validate our methods," says Alex Slepoy from Sandia's Multiscale Computational Materials Methods. "The trick is picking a correct modeling strategy from our toolbox of methods."
Asked whether simulations are merely more complex versions of what a graphic artist produces - a product of the imagination, in short, that cannot accurately produce new details - Slepoy provisionally entertains the idea: "A graphic artist has to make choices that are somewhat subconscious: what size objects to represent, how close-in to zoom, what details to include and exclude, and are there people out there who liked what he drew. So do we.
"But there the similarity ends. For us in computer simulations, the questions are more technical: Does the modeling strategy agree with experiments and is it consistent with established models? Does it have mathematical consistency?"
A further advance in accurate model development, he says, is that "now we're developing automated methods to tell us whether we've satisfied [accuracy] requirements, rather than doing that by just manually looking at results. The method automatically tunes the model to satisfy the entire set of conditions as we know them."
There is also the matter of cost, says Fang: "With smart people developing numerical methods, models, and algorithms to use computers to study real cases, we find we can rerun calculations merely by changing computer parameters. Thus the cost to push science forward is much cheaper than running experiments - particularly in nanoscience, where the realm is so small that experiments are difficult to perform, testing devices are not available, and data acquisition is a challenge."
For all these reasons, he says, "This is why at CINT [the Sandia/Los Alamos Center for Integrated Nanotechnology, funded by DOE's Office of Science], theory and simulation is one of its five thrusts. People view modeling and simulation as a critical component of nanoscience."
"We need to sit back and put our mindset in a different mode," he told his audience. "We're all too busy doing [laboratory] research [instead of considering] how we can leverage resources to push our science to the next level."
Modeling tools include: meso-scale (an intermediate resolution capability functioning between the atomic and macro scales), classical atomistics (classical force-field theory), Density Functional Theory (a one-electron approximation of quantum theory, where an electron interacts with atoms but not with another electron), and the full quantum model (electrons interacting with other electrons and four or five ions).
Neal Singer | EurekAlert!
Interfacial Superconductivity: Magnetic and superconducting order revealed simultaneously
17.01.2017 | Sonderforschungsbereich 668
Manchester scientists tie the tightest knot ever achieved
13.01.2017 | University of Manchester
Researchers from the University of Hamburg in Germany, in collaboration with colleagues from the University of Aarhus in Denmark, have synthesized a new superconducting material by growing a few layers of an antiferromagnetic transition-metal chalcogenide on a bismuth-based topological insulator, both being non-superconducting materials.
While superconductivity and magnetism are generally believed to be mutually exclusive, surprisingly, in this new material, superconducting correlations...
Laser-driving of semimetals allows creating novel quasiparticle states within condensed matter systems and switching between different states on ultrafast time scales
Studying properties of fundamental particles in condensed matter systems is a promising approach to quantum field theory. Quasiparticles offer the opportunity...
Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.
As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...
At TU Wien, an alternative for resource intensive formwork for the construction of concrete domes was developed. It is now used in a test dome for the Austrian Federal Railways Infrastructure (ÖBB Infrastruktur).
Concrete shells are efficient structures, but not very resource efficient. The formwork for the construction of concrete domes alone requires a high amount of...
Many pathogens use certain sugar compounds from their host to help conceal themselves against the immune system. Scientists at the University of Bonn have now, in cooperation with researchers at the University of York in the United Kingdom, analyzed the dynamics of a bacterial molecule that is involved in this process. They demonstrate that the protein grabs onto the sugar molecule with a Pac Man-like chewing motion and holds it until it can be used. Their results could help design therapeutics that could make the protein poorer at grabbing and holding and hence compromise the pathogen in the host. The study has now been published in “Biophysical Journal”.
The cells of the mouth, nose and intestinal mucosa produce large quantities of a chemical called sialic acid. Many bacteria possess a special transport system...
10.01.2017 | Event News
09.01.2017 | Event News
05.01.2017 | Event News
17.01.2017 | Earth Sciences
17.01.2017 | Materials Sciences
17.01.2017 | Architecture and Construction