The Advanced Photon Source
a U.S. Department of Energy Office of Science User Facility

Science Goals: Computational Science and Artificial Intelligence (CAI) Group

Research Tasks
  • Beamline-integrated structural analysis techniques
    • Streaming powder diffraction data reduction (with SRS, Contacts: Von Dreele & Toby)
    • Integrated HEDM data collection and analysis (with MPE, Contact: Sharma)
  • Next-generation computation in support of x-ray experiments
    • Experimental steering enabled by real-time data analysis (Contacts: Bicer & Gürsoy)
    • Analysis of Multimodal Datasets (Contact: Di)
  • Computational Infrastructure
    • Petabyte-scale data management and storage (with SDM & IS/AES): Extrepid deployed (~1.5 Pb)
    • On-demand virtualized high-performance computing (with SDM, SRS, MCS & LCRC): prototype validated
Funded projects
  • Enabling nanometer-scale x-ray fluorescence tomography (PI: Di, ANL/LDRD)
  • Optimization of data-intensive tomography workflows at light sources (PI: Gursoy, LBNL/NESAP)
Theory Projects

X-ray spectroscopy: New theoretical insights have enabled integration of the spectral function and ground-state properties, opening the field of X-ray Magnetic Dichroism (XMD), which allows the study of magnetic materials with polarized x-rays, as well as second order spectroscopies, such as Resonant Inelastic X-ray Scattering (RIXS) and polarized and spin-resolved resonant photoemission. Topics of study include:

  • Relating the various techniques to fundamental materials properties by the derivation of sum rules and theoretical analysis of the cross section. This includes polarization effects.
  • Obtaining a more detailed understanding of second-order spectroscopies. These techniques are often complicated by the presence of the intermediate-state propagator.
  • Time-dependent and nonequilibrium spectroscopy. In recent years, there has been an increased emphasis in measuring x-ray spectra on materials excited by visible or infrared radiation. Our group is developing methodologies to understand time-dependent x-ray spectroscopy on materials away from equilibrium.

Strong electron correlations and magnetism: As a result of direct transitions into the valence shell, x-ray spectroscopy offers a direct probe into the microscopic behavior of strongly correlated and magnetic systems. Although a successful interpretation of spectroscopy can lead to deeper insights into these materials, it often requires detailed modeling of complex materials and phenomena. Our studies in this area include:

  • The calculations of spectral lineshapes with various numerical tools. We have special expertise in the exact diagonalization of small clusters including the full-multiplet Coulomb interaction and spin-orbit coupling, of particular value for the interpretation of transition-metal and rare-earth compounds.
  • Providing a link between the results of x-ray spectroscopy and materials research and theory. Theoretical interpretation is essential to relate the spectral to charge and magnetic excitations, dynamic structure factors, spin polarization, etc.
Software Packages

The CAI group members have developed a number of open source software and data collections, some in collaboration with XSD beamline scientists and external researchers.

  • TomoPy - Package for tomographic data processing and image reconstruction
  • GSAS-II - General purpose crystallographic analysis package
  • MIDAS - Microstructural Imaging from high energy diffraction microscopy
  • XDesign - Package for generating configurable simulation phantoms for benchmarking tomographic image reconstruction.
  • TomoBank - Repository of experimental and simulated tomography data sets with the aim to foster collaboration among computational scientists and experimentalists.
  • DataExchange - Package for an interface among raw tomographic data collected at different light sources and applications.