Transcript Connecting Expt and Theory

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
Advanced Computation
Synchrotron x-ray sources
Currently five CRTs linking scientists at Universities,
National Laboratories and Industry
CI in Europe
European Theoretical
Spectroscopy Facility
nanoquanta
Psi_k
WIEN2k, VASP,
ABINIT, ADF, …
Example 1: Multiple frequency scales:
X-ray Absorption Spectra (XAS)
theory vs expt
fcc Al
arXiv:cond-mat/0601242
http://leonardo.phys.washington.edu/feff/opcons
UV
X-ray
Photon energy (eV)
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!
Ψ
Efficient!
FEFF8 USER FRIENDLY
ab initio XAS Code
Matrix inversion
89 atom cluster
BN
Core-hole, SCF potentials
Essential!
FAST Parallel Computing Algorithms
FEFFMPI
MPI: Natural parallelization G(E)
Each CPU does few energies
Lanczos: Iterative matrix inverse
Smooth crossover between
XANES and EXAFS!
1/NCPU
Impact:
Quantitative
Theory of XAS;
Quantitative
Analysis of EXAFS
and XANES
1000’s of applications
J. J. Rehr & R.C. Albers
Rev. Mod. Phys. 72, 621 (2000)
Impact on Science: Quantitative Theory of
Optical 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
J. Synchrotron Rad. 12,70 (2004)
Combined fit of
XAFS+XANES w/
Approach: Minimize
a priori information
χ2=Σi |μi theory(X) -μi expt|2
Natural separation into
+ xAx (a priori information)
Relevant (Q dominates)
→ [Q + A] x = b
or
Q information matrix
Irrelevant (A dominates)
A a priori matrix
b normalized signal
parameters
x parameters R,N,… μ0
Example 2: Multiple length/time scales
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.
CI: Real Time-TDDFT for Nano-scale systems*
Real space/real time solution to Kohn-Sham equations
Perturbation ΔH(t) = − E · x θ(-t)
*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
FTC(A)
from RT-TDDFT vs experiment
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 for
Combined, 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
λ[ ε(ω) ]
Ab initio Collision Stopping Power
CSP [ ε(ω) ]
FEFF8-MP
FEFF8-MP
arXiv:cond-mat/0605135
Application: New Detector Design (PNNL - DHS)
http://www.leonardo.washington.edu/feff/opcons
Optical Constants FEFF8 vs DESY Tables