The European Theoretical Spectroscopy Facility and the NanoSTAR

Transcription

1 The European Theoretical Spectroscopy Facility and the NanoSTAR Spectroscopy and Nanoscience Valerio Olevano and Alain Pasturel CNRS Institut Néel and INPG SiMaP and CMRS LP2MC

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4 ETSF: some applications

5 Condensed Matter Theories Models: Jellium Anderson Hubbard -> DMFT analytic Semi-Empirical and Phenomenological Theories: Tight Binding LCAO lightly numerical Ab Initio First-Principles or Microscopical Theories: CI QMC DFT, TDDFT MBPT (GW and Bethe-Salpeter Equation) heavy numerical

6 Condensed Matter Theories Models: Jellium Anderson Hubbard -> DMFT analytic Semi-Empirical and Phenomenological Theories: Tight Binding... lightly numerical Ab Initio First-Principles or Microscopical Theories: CI QMC DFT, TDDFT MBPT (GW and Bethe-Salpeter Equation) ETSF heavy numerical

7 Why we need ab initio theories to calculate spectra 1)To understand and explain observed phenomena without conjectures that can reveal wrong; 2)To offer experimentalists reference spectra; 3)To predict properties before the synthesis, the experiment. Theory seen as a Facility to the Experiment and Industry

8 Historical Scientific Fields and Extensions Tight Binding QMC DMFT BSE GW NEGF CI TDDFT DFT

9 Who is ETSF: around 180 scientists 10 node founders: York (coordinator R. Godby) Berlin FU (E.K.U. Gross) Berlin FHI (M. Scheffler) Palaiseau (L. Reining) San Sebastian (A. Rubio) Louvain la Neuve (X. Gonze) Jena (F. Bechstedt) Lund (U. Von Barth, C.-O. Almbladh) Milan (G. Onida) Rome (R. Del Sole) 5 new associated nodes: Palaiseau (A. Georges) Modena (E. Molinari, S. Ossicini) Jyvaskyla (R. Van Leeuwen) Leoben (C. Ambrosch-Draxl) Rhone-Alpes (A. Pasturel) USA Transatlantic Node: (S. Louie, E. Shirley, J. Rehr) Financed by: EU FP7 I3 5M (+ national + local) In France by: Ecole Polytechnique, CNRS, CEA, ANR, Ile de France, RTRA In Belgium (central node): Locals + Long term Positions for Executive Directors Adjoint, 1 Admin, 1 Technician

10 What is the work of an ETSF researcher? We: 1. Develop Analytically the Theory and the Approximations; 2. Implement the Theory in Algorithms and in Computer Codes (in many cases distributed Free Open-Source); 3. Calculate Numerically a wide range of Properties for a wide range of Systems; 4. Compare with the Experiment; 5. Begin to Predict the Experiment.

11 Need for a large scale European structure: ETSF represents: Optimal organization of the work on theory; Sharing of work, know-how and codes among theoreticians; Training of the ETSFacility users (Theoreticians but also Experimentalists and Industrials) on Theory and use of the Codes; Natural interface toward the Experiment and the Technology (Industry).

12 How the ETSF works? The ETSF works like a Synchrotron Experimental Facility: there are 2 call for proposals per year. There are several beamlines and a local contact for each. Valerio Olevano, Institut Neel, CNRS, France

13 NanoSTAR RTRA Grenoble local project Rhône-Alpes ETSF node

14 RTRA NanoSTAR actors CNRS Néel MCMF theory group (D. Mayou, L. Magaud, E.K. Hlil, V. Olevano, X. Blase) INPG SIMaP theory group (A. Pasturel, N. Jakse) UJF DCM theory group (M. Casida) CEA DRFMC L_Sim (F. Lancon, T. Deutsch, P. Pochet, Y.M. Niquet, D. Caliste) CEA DRFMC INAC theory (S. Roche) CEA LETI-MINATEC theory group (P. Blaise, F. Triozon) CNRS LP2MC QMC group (M. Holzmann) 17 permanents!

15 RTRA NanoSTAR 2 scientific axes + numerical resources Spectroscopy: PhD (UJF Casida - CEA Deutsch), New developments of TDDFT on Wavelets for Photochemistry Spectroscopy Quantum Transport: PhD (CNRS Mayou CEA LETI Triozon), Diffusion and Inelastic Effects beyond Kubo-Greenwood in Quantum Transport Numerical Resources: 150kEuros injected on the CIMENT.Phynum platform

16 Theoretical Spectroscopy: some examples

17 EELS TDDFT theory e- c e- electrons ωcv e- v sample Lautenschlager e- c e- e- or ect det v ωp plasmon Valerio Olevano, Institut Neel, CNRS, France

18 TDDFT: fundamental equations 1 =1 v c 0 ABS = Im ε Dielectric Function ε 0 Observables EELS = -Im ε 1 = v c f xc Coulombian (Local-Fields) Polarizability χ Exchange-Correlation Kernel eigenvalues = excitations = poles of χ t ' tt ' at '= 2 at Casida's equation eigenvectors = oscillator strengths

19 Excited state dynamics E. Tapavicza, I. Tavernelli, U. Rothlisberger, C. Filippi, and M.E. Casida, JCP submitted Ground state dynamics 3 CASSCF 7 4 TDPBE TDA How best to model Conical intersections in TDDFT?

20 TDDFT vs EELS plasmon bulk plasmon plasmon V. Olevano and L. Reining PRL (2001) code A. Marinopoulos et al. PRL 89, (2002)

21 Synchrotron Radiation (IXSS) TDDFT X c X rays ωcv v sample ESRF, Grenoble c ctor dete v ωp plasmon Valerio Olevano, Institut Neel, CNRS, France

22 TDDFT vs IXSS synchrotron-radiation spectroscopy plasmon-fano resonance Weissker et al PRL In Solids all Dielectric Properties related to the Energy-Loss function are well described by TDDFT in RPA with an improvement in ALDA.

23 Optical Properties Ellipsometry BSE reflected photon incident photon hν c ωcv v sample transmitted photon Cardona et al. hν dete ctor Valerio Olevano, Institut Neel, CNRS, France

24 TDDFT RPA Optical Properties in Nanotubes A. Marinopoulos et al., (2004) RPA is qualitatively able to interpret observed structures in optical spectra

25 Exciton and Bethe-Salpeter Equation c c c hν EXC ωcv hν ωcv v v RPA GW e- P= h+ Polarisation + hν W ωcv v BSE + + O(2) Valerio Olevano, Institut Neel, CNRS, France

26 Bethe-Salpeter Equation L=GG GG L = / G i v c i W Σ = Self-Energy Bethe-Salpeter Equation Interaction Kernel W =Screened Interaction Valerio Olevano, Institut Neel, CNRS, France

27 BSE vs Optical Spectroscopy Excitonic effects n=1 Exciton Hydrogen En 1/n2 Balmer-like series code n=2 electron-hole n=3 continuum Valerio Olevano, Institut Neel, CNRS, France

28 Photoemission GW theory hν hν e- esample tor sample inverse photoemission de tec direct photoemission hν elure Orsay, Sirotti et al. hν c v e- c v Valerio Olevano, Institut Neel, CNRS, France

29 GW Approximation for the Self-Energy Dynamical Screened Interaction W GW Self-Energy GW x 1, x 2 =i G x 1, x 2 W x 1, x 2 1 Green Function or Electron Propagator G Hartree-Fock Self-Energy x x 1, x 2 =i G x 1, x 2 v x 1, x 2 Valerio Olevano, Institut Neel, CNRS, Grenoble Bare Coulombian Potential v 2

30 PES and ARPES vs GW VO2: Peierls or Mott-Hubbard? M. Gatti et al., PRL 2006 Vanadium Oxide Bandgap HF 7.6 DFT-LDA 0 COHSEX 0.8 GW-COHSEX 0.7 EXP 0.6

31 GW and the Photoemission Band Gap adapted from Shiffelgarde et al. (2006)

32 Nanoelectronics NEGF V lead Left Contact µl conductor Nanoscale Conductor: finite number of states, out of equilibrium, dissipative effects lead Right Contact µr V = L R Macroscopic Reservoirs: continuum of states, thermodynamic equilibrium Mesoscopic Leads: large but finite number of states, partial equilibrium, ballistic We need: a First Principle description of the Electronic Structure for Finite Voltage: Open System and Out-of-Equilibrium description. Valerio Olevano, Institut Neel, CNRS, France

33 C / V in a gold nanochain: NEGF-GW vs EXP e-e e-ph } EXPERIMENT Frederiksen et al., PRL 93, (2004) N. Agrait, PRL 88, (2002) P. Darancet, et al. PRB 75, (2007).

34 Example of a Nanoscale Photoswitch W. Hu et al. J. Am. Chem. Soc. 127, 2804 (2005) Type of problem that could benefit from modeling with TDDFT : Efficiency is important (e.g. Need for wavelet algorithms) 1 Explicit double excitations can be important ( Ag state of polyenes, conical intersections in photoreactions)

35 Conclusions The ETSF represents: Optimal organization of the work on theory; Sharing of work, know-how and codes among theoreticians; Training of the ETSFacility users (Theoreticians but also Experimentalists and Industrials) on Theory and use of the Codes; Natural interface toward the Experiment and the Technology (Industry). Valerio Olevano, Institut Neel, CNRS, France