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Connecting Experiment and Theory across Length and Time-scales
Algorithms and Software for Materials
Research CyberInfrastructure
J. J. Rehr
Department of Physics
University of Washington
Seattle, WA
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Why we need computational theory:
``If I can’t calculate it, I don’t understand it.”
R.P. Feynman
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What’s going on outside NSF in
CI
for computational materials research?
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CI at the DOE CMSN
Currently five CRTs linking scientists at Universities,
National Laboratories and Industry
Advanced Computation Synchrotron x-ray sources
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CI in Europe
European Theoretical Spectroscopy Facility
nanoquanta
Psi_k
WIEN2k, VASP, ABINIT, ADF, …
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Example 1: Multiple frequency scales:X-ray Absorption Spectra (XAS)
Photon energy (eV)
fcc Al
UV X-ray
arXiv:cond-mat/0601242
http://leonardo.phys.washington.edu/feff/opcons
theory vs expt
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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
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Paradigm shift:
Use Green’s functions not wave functions!
Efficient!
Ψ
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FEFF8 USER FRIENDLY ab initio XAS Code
BN
Core-hole, SCF potentials
Essential!
89 atom cluster
Matrix inversion
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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/NCPU
FEFFMPI
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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
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Impact on Science: Quantitative Theory ofOptical Response UV – X-ray
Dielectric function Energy Loss (EELS)
Absorption coefficient
Refractive index
Reflectivity
X-ray scattering factors f = f0 +f1 + if2
Full spectrum Green’s function (FEFF8MPI) codes
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CI: Bayesian Fit to Experiment
Approach: Minimize
χ2=Σi |μi theory(X) -μi
expt|2
+ xAx (a priori information) → [Q + A] x = b
Q information matrix
A a priori matrix
b normalized signal
x parameters R,N,… μ0
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
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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 UWGrant 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
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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.
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Static Limit
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Optical absorption of FTC chromophores from RT-TDDFT vs experiment FTC(A)
FTC(B)
FTC(C)
Expt: L. Dalton et al. (UW)
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CI: New Algorithms for Frequency Dependent Nonlinear response
of large organic photonic chromophores
Response function Re B333(ω)
is related to the imaginary part of the first-order non-linear
polarizability β333.
Nonlinear response of FTC chromophore
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CI Computer-science Nuts and Bolts forCombined, user-friendly codes
• NEED: standard Input/Output protocols e.g. XML I/O new international standard (SIESTA, ABINIT, chemistry CPL …)
• Graphical User Interfaces GUIs e.g. JAVA, PERL or XML based: XFORM – XHTML
• International cooperation (e.g. EU: nanoquanta, CML)
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FEFFML – prototype XML for FEFF
(Yoshi Takimoto, UW)
schema for FEFF output xmu.dat
<feffOutput> <data> <energy>8985.121</energy> <energyWrtEdge>-3.348</energyWrtEdge> <k>0</k> <mu>3.19E-01</mu> <mu0>4.51E-01</mu0> <chi>-1.53E-01</chi> </data> <data> <energy>8985.131</energy> <energyWrtEdge>-3.339</energyWrtEdge> <k>0.05</k>
xmu.xml in Excel
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CI: GUI Development in FEFF (JAVA)
(J. Kas UW)
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Rx 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
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That’s all folks!
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CMSN-ESESRF
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ETSF
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Inelastic losses
Ab initio Inelastic Mean Free Path Ab initio Collision Stopping Power
Application: New Detector Design (PNNL - DHS)
FEFF8-MP
FEFF8-MP
λ[ ε(ω) ] CSP [ ε(ω) ]
arXiv:cond-mat/0605135
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Optical Constants FEFF8 vs DESY Tables
http://www.leonardo.washington.edu/feff/opcons