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 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 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)
xmu.xml in Excel
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
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
λ[ ε(ω) ]
FEFF8-MP
CSP [ ε(ω) ]
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