David Kirkpatrick

February 26, 2010

Quantum physics improving electronics and autos

Or so this news from Princeton purports.

The release:

SCIENTISTS FIND AN EQUATION FOR MATERIALS INNOVATION

Posted Feb 25, 2010By Chris Emery

Professor Emily Carter and graduate student Chen Huang developed a new way of predicting important properties of substances. The advance could speed the development of new materials and technologies. (Photo: Frank Wojciechowski)

Princeton engineers have made a breakthrough in an 80-year-old quandary in quantum physics, paving the way for the development of new materials that could make electronic devices smaller and cars more energy efficient.

By reworking a theory first proposed by physicists in the 1920s, the researchers discovered a new way to predict important characteristics of a new material before it’s been created. The new formula allows computers to model the properties of a material up to 100,000 times faster than previously possible and vastly expands the range of properties scientists can study.

“The equation scientists were using before was inefficient and consumed huge amounts of computing power, so we were limited to modeling only a few hundred atoms of a perfect material,” said Emily Carter, the engineering professor who led the project.

“But most materials aren’t perfect,” said Carter, the Arthur W. Marks ’19 Professor of Mechanical and Aerospace Engineering and Applied and Computational Mathematics. “Important properties are actually determined by the flaws, but to understand those you need to look at thousands or tens of thousands of atoms so the defects are included. Using this new equation, we’ve been able to model up to a million atoms, so we get closer to the real properties of a substance.”

By offering a panoramic view of how substances behave in the real world, the theory gives scientists a tool for developing materials that can be used for designing new technologies. Car frames made from lighter, strong metal alloys, for instance, might make vehicles more energy efficient, and smaller, faster electronic devices might be produced using nanowires with diameters tens of thousands of times smaller than that of a human hair.

Paul Madden, a chemistry professor and provost of The Queen’s College at Oxford University, who originally introduced Carter to this field of research, described the work as a “significant breakthrough” that could allow researchers to substantially expand the range of materials that can be studied in this manner. “This opens up a new class of material physics problems to realistic simulation,” he said.

The new theory traces its lineage to the Thomas-Fermi equation, a concept proposed by Llewellyn Hilleth Thomas and Nobel laureate Enrico Fermi in 1927. The equation was a simple means of relating two fundamental characteristics of atoms and molecules. They theorized that the energy electrons possess as a result of their motion — electron kinetic energy — could be calculated based how the electrons are distributed in the material. Electrons that are confined to a small region have higher kinetic energy, for instance, while those spread over a large volume have lower energy.

Understanding this relationship is important because the distribution of electrons is easier to measure, while the energy of electrons is more useful in designing materials. Knowing the electron kinetic energy helps researchers determine the structure and other properties of a material, such as how it changes shape in response to physical stress. The catch was that Thomas and Fermi’s concept was based on a theoretical gas, in which the electrons are spread evenly throughout. It could not be used to predict properties of real materials, in which electron density is less uniform.

The next major advance came in 1964, when another pair of scientists, Pierre Hohenberg and Walter Kohn, another Nobel laureate, proved that the concepts proposed by Thomas and Fermi could be applied to real materials. While they didn’t derive a final, working equation for directly relating electron kinetic energy to the distribution of electrons, Hohenberg and Kohn laid the formal groundwork that proved such an equation exists. Scientists have been searching for a working theory ever since.

Carter began working on the problem in 1996 and produced a significant advance with two postdoctoral researchers in 1999, building on Hohenberg and Kohn’s work. She has continued to whittle away at the problem since. “It would be wonderful if a perfect equation that explains all of this would just fall from the sky,” she said. “But that isn’t going to happen, so we’ve kept searching for a practical solution that helps us study materials.”

In the absence of a solution, researchers have been calculating the energy of each atom from scratch to determine the properties of a substance. The laborious method bogs down the most powerful computers if more than a few hundred atoms are being considered, severely limiting the amount of a material and type of phenomena that can be studied.

Carter knew that using the concepts introduced by Thomas and Fermi would be far more efficient, because it would avoid having to process information on the state of each and every electron.

As they worked on the problem, Carter and Chen Huang, a doctoral student in physics, concluded that the key to the puzzle was addressing a disparity observed in Carter’s earlier work. Carter and her group had developed an accurate working model for predicting the kinetic energy of electrons in simple metals. But when they tried to apply the same model to semiconductors — the conductive materials used in modern electronic devices — their predictions were no longer accurate.

“We needed to find out what we were missing that made the results so different between the semiconductors and metals,” Huang said. “Then we realized that metals and semiconductors respond differently to electrical fields. Our model was missing this.”

In the end, Huang said, the solution was a compromise. “By finding an equation that worked for these two types of materials, we found a model that works for a wide range of materials.”

Their new model, published online Jan. 26 in Physical Review B, a journal of the American Physical Society, provides a practical method for predicting the kinetic energy of electrons in semiconductors from only the electron density. The research was funded by the National Science Foundation.

Coupled with advances published last year by Carter and Linda Hung, a graduate student in applied and computational mathematics, the new model extends the range of elements and quantities of material that can be accurately simulated.

The researchers hope that by moving beyond the concepts introduced by Thomas and Fermi more than 80 years ago, their work will speed future innovations. “Before people could only look at small bits of materials and perfect crystals,” Carter said. “Now we can accurately apply quantum mechanics at scales of matter never possible before.”

March 14, 2009

Scientists cheer Omnibus Bill

It’s always a good sign for R&D when scientists once again cheer actions from Washington. May the theocrats go hide away in caves and read their fairy tales by the light of candles and campfires.

The release:

APS applauds Senate passage of FY09 omnibus bill

Funding will enable scientists to continue transformational research, leading to innovation, job creation and economic prosperity for the nation

WASHINGTON, D.C. – The American Physical Society (APS) is elated that the Senate has approved the FYO9 Omnibus Bill, which will allow scientists to continue cutting-edge research that will lead to innovation, job creation and economic growth for the United States.

Specifically, APS lauds the bill’s support of research programs at the Department of Energy’s Office of Science, the National Science Foundation and the National Institute of Standards and Technology. Scientists, who receive funding from these agencies, can now further their research on developing solutions to some of the country’s most pressing challenges – developing clean, affordable energy, improving health care and strengthening science and math instruction in our schools.

“At a time when the nation is coping with a deep recession and striving for an economic recovery, federal investments in science and technology are more critical to America’s future than ever,” said Michael S. Lubell, APS director of public affairs. “Crises provide opportunities for creative outcomes. It is gratifying to see science high on Congress’ priority list.”

APS applauds the leadership of Congress and President Obama on the importance of funding science, the seed corn of new discoveries, job growth and economic prosperity for the nation. As policymakers seek solutions to the nation’s many challenges, funding in the FY09 Omnibus Bill, as well as predictable, sustainable increases in the future, will ensure that they can count on scientists to lead in developing those solutions.

 

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About APS: The American Physical Society is the world’s leading professional organization of physicists, representing more than 46,000 physicists in academia and industry in the U.S. and internationally. It has offices in College Park, Md., Ridge, N.Y., and Washington, D.C.

September 21, 2008

American Physical Society announces new online pub

Filed under: Media, Science — Tags: , , , , , — David Kirkpatrick @ 2:21 pm

The e-zine is called Physics, it’s free and will find the gems and provide commentary on papers from Physical Review Letters and Physical Review .

From the link:

The authoritative but brief reports in Physics on exciting and important new research will help keep researchers abreast of developments within and outside of their own fields and can catalyze interdisciplinary work. With the combined output of the APS peer-reviewed publications at about 18,000 papers a year, there is clearly a need to pull the truly exceptional papers out from among the merely excellent works, and place them in context.

“Our readers don’t want to miss significant developments in other subfields of physics,” says Gene Sprouse, APS Editor in Chief, “and our authors need and deserve more attention for their best papers.” Physics aims to meet those needs by means of three features, all with original content. “Viewpoints” discuss and explain a particular paper’s findings in a manner accessible to all physicists, especially to those outside its subspecialty. “Trends” are longer pieces that cover a recent body of work in a specific field, but also look ahead to the challenges and questions that fascinate that field’s top researchers. “Synopses” are staff-written summaries of papers that merit wider attention among physicists in all fields.

“The selection process will be rigorous but not rigid,” says David Voss, Physics’ Editor. “We’ll highlight papers that change the rules of the game, afford cross-disciplinary potential, or report a substantial breakthrough in a particular field.” Feedback and suggestions by email to physics_at_aps.org are welcome.