Nanotechnology Now

Our NanoNews Digest Sponsors

Heifer International

Wikipedia Affiliate Button

Home > Press > Theory aims to describe fundamental properties of materials

Abstract:
Gold is shiny, diamonds are transparent, and iron is magnetic. Why is that?

The answer lies with a material's electronic structure, which determines its electrical, optical, and magnetic properties. Sandia relies extensively on using and controlling such properties, for everything from assuring weapons reliability to creating devices from nanomaterials.

Theory aims to describe fundamental properties of materials

LIVERMORE, CA | Posted on February 15th, 2007

Predicting a material's properties by first calculating its electronic structure would cut down experimental time and might lead researchers to uncover new materials with unexpected benefits.

But commonly used simulations are inaccurate, especially for materials like silicon, whose strongly correlated electrons influence each other over a distance and make simple calculations difficult.

Now a team of researchers at Sandia National Laboratories may have a solution that offers huge potential. Through both internal and Department of Energy Office of Science funding, Sergey Faleev and his colleagues applied theoretical innovations and novel algorithms to make a hard-to-use theoretical approach from 1965 amenable to computation. The team's approach may open the door to discovering new phases of matter, creating new materials, or optimizing performance of compounds and devices such as alloys and solar cells.

Their paper, "Quasiparticle Self-Consistent GW Theory," appeared in the June 9, 2006, issue of Physical Review Letters. GW refers to Lars Hedin's 1965 theory that elegantly predicts electronic energy for ground and excited states of materials. "G" stands for the Greens function used to derive potential and kinetic energy and "W" is the screened Coulomb interaction, which represents electrostatic force acting on the electrons. "Quasiparticles" are a concept used to describe particle-like behavior in a complex system of interacting particles. Self-consistent means the particle's motion and effective field, which determine each other, are iteratively solved, coming closer and closer to a solution until the result stops changing.

"Our code has no approximation except GW itself," said Faleev. "It's considered to be the most accurate of all GW implementations to date."

"It works well for everything in the periodic table," adds coauthor Mark van Schilfgaarde, a former Sandian now at Arizona State University. The paper reports results for diverse materials whose properties cannot be consistently predicted by any other theory. The 32 examples include alkali metals, semiconductors, wide band-gap insulators, transition metals, transition metal oxides, magnetic insulators, and rare earth compounds.

Describing force

"Everything in solids is held together by electrostatic forces," says van Schilfgaarde. "You can think of this as a huge dance with an astronomically large number of particles, 1023, that is essentially impossible to solve. The raw interactions among the particles are remarkably complex.

"Hedin replaced the raw interactions with 'dressing' the particle with a screened interaction," van Schilfgaarde continues, "so the effective charge is much smaller. It becomes much more tractable but the equations become more complicated you have an infinite number of an infinite number of terms. The hope is that the higher-order terms die out quickly."

The researchers' use of GW makes the expansion much more rapidly convergent.

"We're pretty confident we got the approach right," he says. He now would like another group to independently verify this way of framing the task.

Promise and challenges ahead

The researchers use a molecular dynamics code, VASP (Vienna Ab-initio Simulation Package) to model, for example, equations of state in high-energy-density matter. These equations of state depend on quantities like electrical conductivity. Calculating this requires detailed knowledge of the electronic structure a perfect application for Faleev's work. The researchers hope to describe optical spectra, calculate total energy, and account for more than 10 atoms in a unit cell at 100 times the current speed. Accelerating the code would facilitate modeling in other research areas at Sandia, such as simulating titanium dioxide used in surface science, or aiding research into carbon nanotubes that might be used in electronic or optical devices.

"To calculate absorption or optical spectra is a huge problem," Faleev says with anticipation. "To make it faster is a huge problem. To make it more accurate is a huge problem. To incorporate VASP is a huge problem." Van Schilfgaarde agrees. "It's quite an accomplishment to do it at all. It takes someone who is very strong in math, and a clever programmer. We spent easily five to six man-years between us to make it work.

"If we can get the approach right, we can have a theory that's universally accurate for anything we want that's really pretty neat, just requiring knowledge of where the atoms are." Van Schilfgaarde believes the theory's advantage would be to offer true insight into material behavior. "It's kind of like adding night-vision goggles to soldiers working in the dark," he says. "Probably in 10 years," adds Sergey, "everyone will use this."

####

About DOE/Sandia National Laboratories
Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin company, for the U.S. Department of Energy's National Nuclear Security Administration. Sandia has major R&D responsibilities in national security, energy and environmental technologies, and economic competitiveness.

Release and images are available at http://www.sandia.gov/news/resources/releases/2007/material-properties.html

Sandia National Laboratories' World Wide Web home page is located at http://www.sandia.gov . Sandia news releases, news tips, science photo gallery, and periodicals can be found at the News Center button.

For more information, please click here

Contacts:
Mike Janes

925-294-2447

Copyright © DOE/Sandia National Laboratories

If you have a comment, please Contact us.

Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.

Bookmark:
Delicious Digg Newsvine Google Yahoo Reddit Magnoliacom Furl Facebook

Related News Press

Discoveries

Nanoparticle exposure can awaken dormant viruses in the lungs January 17th, 2017

Nanoscale view of energy storage January 16th, 2017

Seeing the quantum future... literally: What if big data could help you see the future and prevent your mobile phone from breaking before it happened? January 16th, 2017

NUS researchers achieve major breakthrough in flexible electronics: New classes of printable electrically conducting polymer materials make better electrodes for plastic electronics and advanced semiconductor devices January 14th, 2017

Materials/Metamaterials

NUS researchers achieve major breakthrough in flexible electronics: New classes of printable electrically conducting polymer materials make better electrodes for plastic electronics and advanced semiconductor devices January 14th, 2017

Manchester scientists tie the tightest knot ever achieved January 13th, 2017

Nanoscale Modifications can be used to Engineer Electrical Contacts for Nanodevices January 13th, 2017

Deciphering the beetle exoskeleton with nanomechanics: Understanding exoskeletons could lead to new, improved artificial materials January 12th, 2017

Announcements

Nanoparticle exposure can awaken dormant viruses in the lungs January 17th, 2017

Nanoscale view of energy storage January 16th, 2017

Seeing the quantum future... literally: What if big data could help you see the future and prevent your mobile phone from breaking before it happened? January 16th, 2017

NUS researchers achieve major breakthrough in flexible electronics: New classes of printable electrically conducting polymer materials make better electrodes for plastic electronics and advanced semiconductor devices January 14th, 2017

Energy

Stability challenge in perovskite solar cell technology: New research reveals intrinsic instability issues of iodine-containing perovskite solar cells December 26th, 2016

Nanoscale 'conversations' create complex, multi-layered structures: New technique leverages controlled interactions across surfaces to create self-assembled materials with unprecedented complexity December 22nd, 2016

Safe and inexpensive hydrogen production as a future energy source: Osaka University researchers develop efficient 'green' hydrogen production system that operates at room temperature in air December 21st, 2016

Going green with nanotechnology December 21st, 2016

NanoNews-Digest
The latest news from around the world, FREE




  Premium Products
NanoNews-Custom
Only the news you want to read!
 Learn More
NanoTech-Transfer
University Technology Transfer & Patents
 Learn More
NanoStrategies
Full-service, expert consulting
 Learn More











ASP
Nanotechnology Now Featured Books




NNN

The Hunger Project