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