Cooperative Research Teams

Click on the links below for a brief description of the scientific goals of each team.

Resonant Inelastic X-Ray Scattering

Principal Investigators:

Resonant elastic and inelastic x-ray scattering have the potential to become two of the most powerful experimental probes of strongly correlated electronic systems. These probes directly couple to the two-particle excitations of highly correlated materials and are unique in providing both energy and momentum resolution: resonant x-ray scattering can image exotic ordering such as orbital or magnetic ordering; and resonant inelastic x-ray scattering can directly image the charge excitation spectra for all momenta. Unfortunately, experimental progress has been limited due to the fact that these probes involve complicated many-body processes and, for example, the meaning of different spectral peaks and how they disperse are not well understood. Even less is known about how to correlate the experimental data with the underlying microscopic low-energy models of the strongly correlated electrons. Our cooperative research team (CRT) proposes to significantly enhance the understanding of resonant x-ray scattering techniques both inelastic and elastic to allow for a more rigorous interpretation and use of the experimental data.

Our approach begins by combining the best aspects of the three different computational techniques currently used to interpret x-ray scattering — density functional theory, dynamical mean-field theory, and small-cluster exact diagonalization — to achieve a more realistic material-specific picture of the interaction between x-rays and complex matter. Our study will convert resonant x-ray scattering into a major experimental tool by providing a better understanding of the role of charge correlations in materials where many degrees of freedom are intertwined. Our initial focus is on the cuprates and other strongly correlated transition-metal compounds, which are of great current interest and where most experiments have been or will soon be performed.

Our team includes both US and international researchers and is designed to foster new collaborations between researchers currently working with different approaches. In addition, we will develop close relationships with many experimental groups in the U.S. The members of our CRT will collaborate vigorously, across and within our three technical groups, towards the common goal of realistically modeling the resonant x-ray scattering processes in correlated systems. We will create codes to analyze and interpret a wide range of x-ray scattering spectroscopies phenomena which will be openly distributed to the scientific community at large.

CRT Participants

Dynamics and Cohesion of Materials Interfaces and Confined Phases Under Stress

Principal Investigators:

This project brings together a team of researchers with a highly successful record of collaboration under previous CMSN support, to address new and outstanding scientific issues related to the properties of grain boundaries and associated confined interfacial liquid phases under stress. The project addresses challenging new methodological developments required to understand at a fundamental level the physics governing complex interface dominated processes associated with the breakdown of crystal cohesion and failure of stressed polycrystalline materials. This new focus represents a natural extension, and stronger unification, of the team's previous collaborations examining grain boundary and solid-liquid interface properties and their role in governing microstructure evolution. In the currrent project, development and validation of multiscale simulation methodologies are being undertaken in the context of four technologically important and thematically linked processes relevant to the processing and lifetime of materials for diverse DOE-related applications ranging from energy generation to stockpile stewardship. Specifically, we are seeking to gain new insights into the mechanisms of whisker growth, liquid-metal embrittlement, hot tearing and hot-ductility-dip cracking, with an overall goal of developing predictive models to aid in the prevention or control of these phenomena in practical applications.

Project Web site
Publications

Multiscale Simulation of Thermo-mechanical Processes in Irradiated Fission-reactor Materials

Principal Investigators:

Overview: The objective of this Computational Materials Science Network (CMSN) project on Multiscale Simulation of Thermo-mechanical Processes in Irradiated Fission-reactor Materials is to merge the expertise in the simulation of damage cascades in single crystals with the expertise in multiscale simulation of microstructural evolution in polycrystalline materials. This will enable us to elucidate the thermo-mechanical behavior of model fission-reactor materials under irradiation across all the relevant length- and time-scale regimes, with particular focus on the complex interplay between irradiation effects and materials microstructure. Phenomena to be studied include the coupling of irradiation, for example, with phase behavior and precipitation, diffusion creep, fission-gas bubble formation and migration through the microstructure, grain growth, embrittlement and crack propagation. The predictive, materials-physics-based simulation capability to be developed under this coordinated, multi-institutional thrust provides the methodology to systematically elucidate microstructural processes and parameters as input into higher-level, applied types of simulation codes for nuclear-fuel modeling.

Project Web Site
CRT Participants
Talks

Predictive Capability for Strongly Correlated Systems

Principal Investigators:

There are classes of materials that are important to DOE and to the science and technology community in general which have proven very difficult to understand and to simulate in a material-specific manner. These range from actinides, which are central to the DOE mission, to transition metal oxides, which include the most promising components of new spin electronics applications, to intermetallic compounds whose quantum critical behavior has given rise to some of the most active areas in condensed matter theory. After decades of study from a variety of often quite approximate viewpoints, a material-specific, predictive capability for many of these correlated electron systems is now a realistic goal. This exciting possibility is based on (1) new theoretical innovations, (2) coupling of experts in many-body theory with electronic structure practitioners, and (3) development of novel computational algorithms to solve the resulting equations. These new capabilities are arising at a time when there are extensive and novel experimental probes to provide data for a theory-computation-experiment feedback loop that enables the most rapid progress, and also extended computational power to bring to bear on solving the resulting numerical problem. The objective of the proposed cooperative research team is to assemble the required expertise into a coherent team and focus on the application of these new methodologies to the specific issue of Mott transitions, multi-electron magnetic moments, and dynamical properties of correlated materials. The goals are (i) to provide specific, detailed understanding of the complex correlation effects in strongly correlated systems, with specific emphasis on our compound of choice - MnO - through the application and further development of formal methods and numerical algorithms, and (ii) to make available to materials modelers efficient and accurate computer codes, which can then be used more widely for strongly correlated systems. Success in this undertaking will have a clear impact by moving the community toward the longer-term goal of opening up the entire periodic table to simulations with predictive capability.

Project Web Site
 Publications

Predictive Modeling of the Growth and Properties
of Energy-Relevant Thin Films and Nanostructures

Principal Investigators:

This CRT brings together a team of leading researchers with highly complementary expertise and a proven record of collaboration in order to address fundamentally important and computationally challenging issues in the broad areas of thin film growth and nanostructure formation, with emphasis on novel materials for renewable energy applications. The research thrusts are divided into two areas. The first area studies key materials and related computational issues in solar energy conversion for photovoltaic (PV) applications and water splitting via photocatalysis. Materials issues include semiconductor thin films with controlled morphology, dopant distributions, and band gaps. Control of thin film structure during growth is crucial to achieving high-performance materials in cost-effective PV and photocatalysis applications. In multijunction solar cells, the control of dislocations is the key to further enhancement of cell efficiency; in polycrystalline PV thin films, grain boundaries and point defects may limit the performance of the systems. Predictive calculations provide a valuable tool for understanding the properties of these defects. Development of predictive theoretical techniques for such complex systems under nonequilibrium growth conditions demands a highly synergetic team effort of members covering different materials issues and length and time scales.

The second area is the first-principles-based design of novel nanomaterials for energy storage. We will focus on two systems in this area: quantum metallic alloy films for hydrogen storage and novel carbon-based nanomaterials for energy applications. In the first system, we will capitalize on the recent advances in precise control of the growth morphology of metal films in the quantum regime and use the tunable electronic densities at the Fermi level to tailor chemical reactions on the surfaces of such quantum catalysts for efficient decomposition of molecular hydrogen and high-capacity hydrogen storage. The second class of model systems will concern predictive design of light-element-based nanomaterials, such as charged or metal-coated fullerenes and carbon nanotubes, metal-organic frameworks, as potential high-capacity hydrogen storage media. Here the challenge is to describe reliably the interaction energies of different natures, including weak/physical (van der Waals), chemical (Kubas), and/or electrostatic, between the molecular/atomic hydrogen and the nanoscale catalysts or storage materials. Success in this area calls for team efforts of complementary expertise. The proposed research highly complements ongoing BES research programs and will be performed in close interaction with experimentalists for validation of conceptual advances, with the objective of advancing fundamental science in these areas.

Project Web Site
 CRT Participants

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Last update: 18-Nov-2008