Collaborative 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
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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 multi-junction 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
Project Participants
Publication
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Structure and Dynamics of Water and Aqueous Solutions in Materials Science

Principal Investigators:

This project will assemble a Collaborative Research Team to carry out a multifaceted investigation of the structure and dynamics of water and aqueous solutions, as probed by modern pulsed neutron sources and synchrotron radiation techniques. The CRT includes members with expertise in simulations of aqueous solutions using classical and ab initio molecular dynamics techniques and statistical physics, and others with expertise in theoretical spectroscopy calculations in complex systems. The team also includes experimentalists with expertise in x-ray and neutron diffraction, infrared absorption and inelastic scattering techniques probing the molecular dynamics, and modern optical and x-ray spectroscopic techniques probing valence and core electron excitations.

The structure and dynamics of water is a subject of significant controversy due to difficulties in the experimental interpretation and to severe theoretical challenges. The latter include the difficulty of modeling accurately the molecular interactions within first-principle density functional theory, the importance of nuclear quantum effects, and the inadequacy of the independent particle model to describe electronic excitations. These difficulties are further exacerbated by the large role played by disorder and the need for accurate configurational sampling. The CRT will address all the above issues by developing novel methodologies to deal with nuclear quantum motion and to make feasible simulations with accurate functionals including dispersion interactions, and by developing new and efficient algorithms to compute electron excitation spectra beyond the independent particle model for large system sizes.

By addressing these issues this project aims at solving a major open problem in computational materials science, that is the development of robust and predictive tools for the simulation of multiple properties (structural, electronic and vibrational) of liquid water. The validation of the theory and simulation tools developed by the CRT will entail comparisons with some of the most advanced experiments carried out at DOE facilities (including the ALS, SLAC, and ORNL) to study water as a bulk medium, at interfaces and as a solvating medium. In view of the importance of water and aqueous solutions in chemistry, physics, materials and the life sciences, the progress made in this project will impact all these disciplines.

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Computational Design of Fe-based Superconductors

Principal Investigator:

Project Team:

We will develop advanced DMFT based methodologies for first principles studies of correlated materials. Tools for computation of photoemission spectra, optical conductivities, total energies, superconductive spectral functions and pairing interactions will be developed and tested in simple materials such as iron and then will be used to explore the physics of the recently discovered iron pnictides materials. The approach draws on the strengths of different electronic structure methods, such as DFT and GW which will serve as platforms to add DMFT. The team includes experts from the electronic structure, many body communities and will deliver novel many-body based tool for virtual material simulations of unconventional superconductors.

Project Web Site
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Disorder-Mediated Properties of Functional Materials

Principal Investigator:

Project Team:

This CMCSN team aims at making significant advances in the current state-of-the-art theoretical/computational study of disorder in functional materials with energy-related applications, by combining complementary talents, skills, and capabilities into well-organized team efforts within a carefully monitored network. The proposed scenario includes application of existing methods to the timely study of real materials, and fundamental development of new theory and computational schemes to better address the underlying physics of localization and correlation at the nano-scale. Aiming for significant advances, several complementary methodologies will be explored. One thrust is to stretch the accurate length scale via multi-scale many-body approach, by applying perturbation theory to the intermediate length scale, longer than size of the cluster. A complementary thrust is based on beyond-mean-field ensemble self-average over large number of disorder configuration of large length scale. This thrust would provide an independent and complementary comparison to the first thrust. In addition to the methodology development, equally important is to apply currently available method to real materials of importance, for example the complete effects of doping and vacancy in the high-temperature cuprates and the recently discovered iron-pnictides.

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Last update: 23-Sep-2010