1. Connecting Experiment and Theory across Length and Time-scales Algorithms and Software for Materials Research C yber I nfrastructure J. J. Rehr Department of Physics University of Washington Seattle, WA

2. Why we need computational theory: ``If I can’t calculate it, I don’t understand it.” R.P. Feynman

3. What’s going on outside NSF in CI for computational materials research?

4. CI at the DOE CMSNCMSN Currently five CRTs linking scientists at Universities, National Laboratories and Industry Advanced Computation Synchrotron x-ray sources

5. CI in Europe E uropean T heoretical S pectroscopy F acility n anoquanta Psi_k WIEN2k, VASP, ABINIT, ADF, …

6. Example 1: Multiple frequency scales: X-ray Absorption Spectra (XAS) Photon energy (eV) fcc Al UVX-ray arXiv:cond-mat/0601242 http://leonardo.phys.washington.edu/feff/opcons theory vs expt

7. CI: New Theory/Algorithm development: Green’s Function Codes ● Beyond Ground State Density Functional Theory and Quasiparticles ● Inelastic losses, self-energy Σ, vibrations, … ● Core-hole effects + Σ

8. Paradigm shift: Use Green’s functions not wave functions! Efficient! Ψ

9. FEFF8 USER FRIENDLY ab initio XAS Code BN Core-hole, SCF potentials Essential! 89 atom cluster Matrix inversion

10. FAST Parallel Computing Algorithms MPI: Natural parallelization G(E) Each CPU does few energies Lanczos: Iterative matrix inverse Smooth crossover between XANES and EXAFS! 1/N CPU FEFFMPI

11. J. J. Rehr & R.C. Albers Rev. Mod. Phys. 72, 621 (2000) Impact: Quantitative Theory of XAS; Quantitative Analysis of EXAFS and XANES 1000’s of applications

12. Impact on Science: Quantitative Theory of Optical Response UV – X-ray Optical Response Dielectric function Energy Loss (EELS) Absorption coefficient Refractive index Reflectivity X-ray scattering factors f = f 0 +f 1 + if 2 Full spectrum Green’s function (FEFF8MPI) codes

13. CI: Bayesian Fit to Experiment Approach: Minimize χ 2 =Σ i |μ i theory (X) -μ i expt | 2 + xAx (a priori information) → [Q + A] x = b Q information matrix A a priori matrix b normalized signal x parameters R,N, … μ 0 J. Synchrotron Rad. 12,70 (2004) Natural separation into Relevant (Q dominates) or Irrelevant (A dominates) parameters Combined fit of XAFS+XANES w/ a priori information

14. Real time approach for non-linear optical response in nano-scale systems Photonics Devices Y. Takimoto, F. Vila, and J. J. Rehr Supported by NSF Science and Technology Center at UW Grant DMR-0120967 (Y.T. and F.V) and DOE Grant DE-FG02-97ER45623 (JJR) and facilitated by the DOE CMSN. Example 2: Multiple length/time scales

15. CI: Real Time-TDDFT for Nano-scale systems* Perturbation ΔH(t) = − E · x θ(-t) Real space/real time solution to Kohn-Sham equations *TDDFT extension of SIESTA (LCAO Basis) A.Tsolakidis, D. Sanchez-Portal and R.M. Martin, Phys. Rev. B 235416 (2002); extended by Y. Takimoto et al.

16. Static Limit

17. Optical absorption of FTC chromophores from RT-TDDFT vs experiment FTC(A) FTC(B) FTC(C) Expt: L. Dalton et al. (UW)

18. CI: New Algorithms for Frequency Dependent Nonlinear response of large organic photonic chromophores Response function Re B 333 (ω) is related to the imaginary part of the first-order non-linear polarizability β 333. Nonlinear response of FTC chromophore

19. CI Computer-science Nuts and Bolts for Combined, user-friendly codes NEED: standard Input/Output protocols e.g. XML I/O new international standardXML (SIESTA, ABINIT, chemistry CPL …) Graphical User Interfaces GUIs e.g. JAVA, PERL or XML based: XFORM – XHTMLJAVA International cooperation (e.g. EU: n anoquanta, CML)

20. FEFFML – prototype XML for FEFF XML (Yoshi Takimoto, UW) schema for FEFF output xmu.dat 8985.121 - 3.348 0 3.19E-01 4.51E-01 -1.53E-01 8985.131 - 3.339 0.05 xmu.xml in Excel

21. CI: GUI Development in FEFF (JAVA)JAVA (J. Kas UW)

22. R x CI for MR Theory Develop user-friendly codes for materials research Combined ground state, excited state, & analysis codes Condensed matter toolkit Develop Quantitative understanding of excited states Linking theory and experiment across length & time scales Quantitative Interpretation of Spectra Train high-performance-computation savvy grad students and postdocs

23. That ’ s all folks!

24. CMSN-ESESRF

25. ETSF

26. Inelastic losses Ab initio Inelastic Mean Free Path Ab initio Collision Stopping Power Application: New Detector Design (PNNL - DHS) FEFF8-MP λ[ ε(ω) ] CSP [ ε(ω) ] arXiv:cond-mat/0605135

27. Optical Constants FEFF8 vs DESY TablesTables http://www.leonardo.washington.edu/feff/opcons