Materials and Chemistry Theory@ORNL

Oak Ridge National Laboratory in cooperation with the U.S. Department of Energy conducts a broad range of theoretical research in materials sciences and chemistry. This work is tightly integrated with experimental programs and involves development and application of advanced theoretical methods and utilizes some of the world's fastest computers to solve some of the most pressing energy challenges facing our nation.

Techniques employed include first principles methods based on density functional theory, quantum chemistry, classical and ab initio molecular dynamics, transport theory, many body theory, quantum Monte Carlo, phase field analysis and statistical mechanics. Solutions to the pressing energy challenges that ORNL undertakes often require a combination of two or more theoretical approaches in conjunction with with experimental work. Many of these techniques are broadly applicable across wide ranges of chemistry and materials. As such, theory at ORNL often plays a cross-cutting role, with ORNL theorists bridging different areas of energy research.

What is Theory:

Theory is about understanding, prediction, exploration of new conditions before they are realized in the laboratory and drawing connections between experimental observations. Theory at ORNL impacts our programs through prediction of new phenomena, interpretations of experimental results, and by providing novel directions for discovering new materials and chemical systems.

ORNL has a full range of theory activities. These range from basic energy science aimed at laying the ground-work for long term solutions to our energy problems to near term work addressing our nation's most pressing energy and security needs.

Cray X1 supercomputer installed at ORNL. ORNL and the National Center for Computational Sciences are consistently is among the top open research computer centers world wide in terms of capacity.

Capabilities and Infrastructure:

ORNL scientists apply a wide range of methods ranging from analytic methods to simulations on the world's fastest computers. These include numerical solution of quantum many body models, first principles calculations with chemical specificity, and continuum modeling. Often solutions to challenging problems are found only by combinations of approaches.

The laboratory has strong computational capabilities, including group level computers and clusters, midrange institutional clusters with hundreds of processors, and some of the world's fastest supercomputers. We benefit from codes and algorithms developed at ORNL by the Office of Advanced Scientific Computing Research.

Fermi surface of LaFeAsO, parent of the iron based high temperature superconductors, as obtained within density functional theory. Superconductors may allow low loss electricity distribution, a more reliable electric grid and more efficient motors and generators.

Fundamental Energy Research:

ORNL carries out a broad range of fundamental research aimed at expanding the scientific foundations for new, better and more environmentally friendly energy technologies. New characterization tools such as the Spallation Neutron Source and advanced imaging methods are allowing researchers to explore matter at previously unthinkable scales. Theory plays a key role in these efforts by providing understanding of observations, predictions to be tested by experiment and by suggesting novel experiments.

Theory and Materials Discovery:

One of the most pressing needs for energy technology is the discovery of new advanced materials. Traditionally, this involved exploring compositions guided by chemical intuition, experience and general principles. Nowadays, first principles calculations can greatly accelerate this process by providing atomic level understanding of phenomena and predictions of chemical trends. The ORNL program makes extensive use of these methods in conjunction with experiments.

Nanomaterials:

Nanomaterials and new phenomena that only exist at the nanoscale offer the potential for solving some of the most demanding energy problems we face. Developing these technologies will require answering scientific questions such as: How do we predict the properties of nanostructured Materials? What nanostructures will display different and useful properties? How do we synthesize desired nanomaterials? As such, theory plays a particularly important role in nanoscience. Applications at ORNL include designing nanostructures for novel sensors, hydrogen storage and nanoscale electronic devices.

Transportation:

As a sector, transportation provides our nation's greatest opportunities for energy savings. Achieving these savings while maintaining the quality, safety and convenience afforded by current technologies requires high technology gee-whiz advances that are at the same time cost-effective and amenable to large scale manufacturing. At ORNL theory is integrated into experimental programs seeking new advanced materials and processes for engine components, waste heat recovery, catalysts, advanced batteries and the storage and utilization of hydrogen fuel. Recent accomplishments include the prediction of low cost thermoelectric materials for waste heat recovery as well as new materials for hydrogen storage.

Structural Materials:

ORNL has a long history of innovation in structural materials, including high temperature superalloys that have revolutionized turbine design, dispersion hardened steels, structural ceramics and light-weight materials for transportation applications. Theory plays an important role in the ORNL effort. Examples include studies of dislocations, anti-phase boundaries, stacking faults and failure mechanisms in intermetallic compounds and alloys, and first principles investigation of the structure and chemistry of intergrain regions in ceramics. Theory is also being used to provide atomic scale microscopic understanding of the mechanisms of hydrogen embrittlement.

Energetics and structure of the amphoteric O-H complex in CdTe. This complex was found to be important in obtaining carrier compensation essential for (Cd,Zn)Te based spectroscopic radiation detection. This capability is needed in homeland security and nuclear non-proliferation missions.

Understanding and controlling the behavior of materials under extreme conditions, such as high temperature and high radiation flux will be important in future energy technologies, such as next generation nuclear reactors and fusion reactors. Theory plays a crucial role in these activities because of the difficulty and long times needed for experimental studies. Dynamical simulations of radiation events and healing of radiation damage in structural materials under various conditions have yielded important insights into the mechanisms of radiation damage and ways of mitigating them.

National Security and Non-Proliferation:

Theory and modeling at ORNL are used to support the development of novel chemical and biological sensors for national security and homeland defense applications. This includes the design of nanoscale sensors in areas such as explosive detection.

The laboratory maintains a substantial theory effort integrated with experimental activities in the ORNL Center for Radiation Detection Materials and Systems. This effort uses first principles and other approaches in finding ways to improve materials for spectroscopic gamma ray detection and neutron detection and imaging for nuclear non-proliferation and other applications.

For further information:

G.M. Stocks, Materials Theory Group Leader, stocksgm@ornl.gov

M.V. Buchanan, Associate Laboratory Director, buchananmv@ornl.gov

Images courtesy of P.R.C. Kent, R.E. Stoller, G.M.S. Stocks, M.H. Du and D.J. Singh.