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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
Why we need computational theory:
``If I can’t calculate it, I don’t understand it.”
R.P. Feynman
What’s going on outside NSF in
CI
for computational materials research?
CI at the DOE CMSN
Currently five CRTs linking scientists at Universities,
National Laboratories and Industry
Advanced Computation Synchrotron x-ray sources
CI in Europe
European Theoretical Spectroscopy Facility
nanoquanta
Psi_k
WIEN2k, VASP, ABINIT, ADF, …
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
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
Paradigm shift:
Use Green’s functions not wave functions!
Efficient!
Ψ
FEFF8 USER FRIENDLY ab initio XAS Code
BN
Core-hole, SCF potentials
Essential!
89 atom cluster
Matrix inversion
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
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
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
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
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
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.
Static Limit
Optical absorption of FTC chromophores from RT-TDDFT vs experiment FTC(A)
FTC(B)
FTC(C)
Expt: L. Dalton et al. (UW)
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
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)
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
CI: GUI Development in FEFF (JAVA)
(J. Kas UW)
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
That’s all folks!
CMSN-ESESRF
ETSF
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
Optical Constants FEFF8 vs DESY Tables
http://www.leonardo.washington.edu/feff/opcons