Theory and computation of electronic excitations in condensed matter systems, and the ETSF project

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Theory and computation of electronic excitations
in condensed matter systems, and the ETSF project

• G. Onida, N. Manini, L. Molinari, E. Mulazzi, A.
  Bordoni,
• K. Gaál-Nagy, A. Incze, L. Caramella, M.
  Cazzaniga, E. Ponzio,
• and M. Gatti
•  
• Dipartimento di Fisica and INFM, Università di
  Milano
• LSI-SESI,Ecole Polytechnique, Palaiseau, France

• Why excited state ab-initio calculations?
• Theory State-of-the-art, and recent
  developements (mostly density-based)
• Examples solids, clusters, surfaces
• The European Theoretical Spectroscopy Facility

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Why excited states? -Spectroscopies
(experimental characterization)
C20
H. Prinzbach et al. Nature 407, 60 (2000)
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Why excited states? -Useful response to
excitations (1)
Photoluminescence in nc-SiH films

• RT PL excited with a He-Cd laser

c. 2.5 eV
c. 0.6 eV
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Why excited states? -Useful response to
excitations (2)
Optical properties of Ge-Te alloys
Not just academic interest!
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Why excited states? -Useful response to
excitations (3)
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Why ab-initio?

• first principles no parameters (ingredients
  N,Z)

Just solve Schroedinger equation!

• predictivity (new esperiments, new materials)
• access to details which are difficult to obtain
  experimentally
• useful to design materials with the desired
  properties
• generality, transferability, accuracy

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Surface optical reflectivity - study of
anisotropy spectra
Tools to analyse the calculated spectra
Layer-by-layer spectrum decomposition
example Si(100)(2x1)
C.Hogan, R. Del Sole, and G.Onida, PRB 68, 035405
(2003)
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ab-initio methods
First principles calculations theory without
free parameters
YY(r1,r2,.....,rN) ?
Spectroscopy one needs also the

• excited electronic states
• C.I. (Quantum Chemistry)
• Greens functions
• (1965--gt80--gttoday)

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Which excitations?
theory
hn
hn
optical
probe
electronic
electron energy-loss
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• Photoemission

The algebraic sum of the EQP measured in
photoemission and inverse photoemission yields
the quasiparticle gap (Egap-QP)
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What is an absorption spectrum?
c
v
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Independent quasiparticles and transitions?
c
hn
v
P P0 -iGG
Im e ?vc ltvDcgt2 d (Ec-Ev-?)
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Absorption spectrum of Solid Argon
IP-RPA calculation (Independent Quasiparticles)
P P0 -iGG
Excitons?
Im e ?vc ltvDcgt2 d (Ec-Ev-?)
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Absorption spectrum of Solid Argon
Calculation with excitonic effects (G2 via the
Bethe-Salpeter equation)
Im ? ?? ?vcltvDcgt A?vc2 d (E?-?)
V. Olevano (2000)
-gtMixing of transitions -gtModification of
excitation energies
Onida Reining Rubio RMP 74, 601 (2002)
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Back to density functionals?
G. Onida, L. Reining, A. Rubio, Reviews of
Modern Physics 74, 601 (2002)
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Effects of oxidation on small Silicon
nanoaggregates
Oxygen on Si10H16
Ground state equilibrium structure (Density
Functional calculation)
16.000 steps13.5 ps
M. Gatti and G. Onida, PRB 72, 1 (2005)
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Redshift (in eV) of the optical gap of Si10H16
after oxidation
Excited state calculations within TDDFT
(adiabatic LDA approximation)
Silanone (H2SiO)
Silane (SiH4)
Absorption spectra TDLDA works better for
clusters (finite systems) than for infinite
solids.
M. Gatti and G. Onida, PRB 72, 1 (2005)
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Stokes shift relaxation
H2SiO
FIG. 1. Schematic representation of a Stokes
shift relaxation. In position (1), the cluster is
in its electronic ground state, and the atomic
geometry is relaxed to its lowest energy
configuration. On absorption of a photon, the
nanocluster undergoes a vertical electronic
excitation from (1) to (2). Once in the excited
electronic state, the atomic geometry of the
cluster relaxes to a lower energy configuration
from (2) to (3). Finally, the excited electron
and hole recombine via another vertical
transition, (3) to (4). The Stokes shift is
defined as EA - EE (Degoli et al., PRB 69,
155411, 2004)
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Oxydized Si(100) surface
Ground State Calculations
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Optical properties of Si(100)O (0.5 ML)
A. Incze, R. De Sole, G. Onida, PRB 71, 035350
(2005)
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Surface Optical Spectra of Si (100)O as a
function of O coverage
A. Incze, R. De Sole, G. Onida (2005)
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Optical properties of Si (113) (3x2) ADI
Bulk Anisotropy due to the very asymmetric unit
cell and the limited thickness of the slab.
Very difficult to get converged spectra (K.
Gaal-Nagy, G.O. et al, in preparation)
Structure from Stekolnikov, Furthmueller and
Bechstedt, PRB 68, 205306 (2003) PRB 67,
195332 (2003).
In this case, the slicing technique is essential!
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NANOQUANTANETWORK Nanoscale photon absorption
and spectroscopy with electrons
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NANOQUANTA Industrial Advisory Board
-Siemens Medical Solutions, Forcheim (Germany)
Dr. Martin Petersilka, Dr. Thomas von der Haar
-Thales Research and Technology, Orsay (France)
Dr. Nguyen Van Dau, magnetic devices -Labein
Centro Tecnologico, Bilbao (Spain) Dr. Roberto
Garcia, General Manager -Max-Lab, Lund
(Sweden), Dr. Nils Martensson -Materials
Design s.a.r.l., Le Mans (France) Dr. Erich
Wimmer, president -Telefonica Moviles, Madrid
(Spain) Dr. Igacio Camarero, Exec. director of
Technology Operations Support -Acreo AB,
Kista (Sweden) Dr. Jan Y. Andersson, manager
of the Optical Engineering dept -Innovent
Technologieentwicklung, Jena (Germany) Dr.
Detlef Stock -SchottGlas, Mainz (Germany)
Dr. Wolfgang Mannstadt, Dr. Dirk Sprenger.
provisional list
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Lasting integration is needed!
ETSF (European Theoretical Spectroscopy
Facility) will offer

• know-how (e.g., TDDFT theory implementations)
• tools, computer codes
• complementarity of groups (methods, systems)

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• Distributed
• Open

KNOWLEDGE
(European Theoretical Spectroscopy Facility)
Collaborate, Publish
Train
Motivate
Develope and Distribute
Undergraduates PhD Students Post Docs Other
colleagues
Public awareness
Papers Reviews Books
Formula Computer Codes
Let a larger community have access
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How will the ETSF work?
The ETSF will be a large facility It will have
code-and theory-lines It will have users who
present projects
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TOSCA - Tools for Optical Spectra Calculation and
Analysis
Web page users.unimi.it/etsf
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Conclusions

• Ab-initio theoretical spectroscopy
• quantitative and predictive calculations
• answers to new needs, due to new experiments
• We are living a period of strong and fascinating
  growth of new (density-based) theoretical tools
• International integration of resources (Theory,
  knowledge and computer codes) is needed
• NANOQUANTA is today a reality the present
  challenge is to build ETSF. We are on the way.

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Web references

• users.unimi.it/etsf
• google just search nanoquanta
• www.abinit.org

Thank you for your attention !
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Si10H16
(Ground-state adiabatic dynamics)
Microcanonical _at_ 700K
Car-Parrinello Molecular Dynamics
simulation (G.Onida and W. Andreoni, Chem.
Phys. Lett. 243, 183 (1995)
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Nanotubes are transparent for light polarized in
the direction orthogonal to the tube!!
Marinopoulos, Reining, Rubio, Vast, Phys. Rev.
Lett. 91, 046402 (2003)
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NANOQUANTA Industrial Advisory Board
-Siemens Medical Solutions, Forcheim (Germany)
Dr. Martin Petersilka, Dr. Thomas von der Haar
-Thales Research and Technology, Orsay (France)
Dr. Nguyen Van Dau, magnetic devices -Labein
Centro Tecnologico, Bilbao (Spain) Dr. Roberto
Garcia, General Manager -Max-Lab, Lund
(Sweden), Dr. Nils Martensson -Materials
Design s.a.r.l., Le Mans (France) Dr. Erich
Wimmer, president -Telefonica Moviles, Madrid
(Spain) Dr. Igacio Camarero, Exec. director of
Technology Operations Support -Acreo AB,
Kista (Sweden) Dr. Jan Y. Andersson, manager
of the Optical Engineering dept -Innovent
Technologieentwicklung, Jena (Germany) Dr.
Detlef Stock -SchottGlas, Mainz (Germany)
Dr. Wolfgang Mannstadt, Dr. Dirk Sprenger.
provisional list
36
How will the ETSF work?
The ETSF will be a large facility It will have
code-and theory-lines It will have users who
present projects
37
TOSCA - Tools for Optical Spectra Calculation and
Analysis
Web page users.unimi.it/etsf
38
Why excited states? -Useful response to
excitations (2)
Optical properties of Ge-Te alloys
Not just academic interest!
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Back to density functionals?
Static DFT minimization of E
Ground state
Time-Dependent DFT
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Nanoquanta Consensus