Optics

What do we calculate?

• Linear optics (dielectric functions, absorption spectra, cross sections, reflectance anisotropy, surface differential reflectivity, birefringence, chirality).
• Second Harmonic Generation (SHG).

Which systems do we study?

• Surfaces, dots, wires, nanotubes, molecules (isolated and in environment).
• Bulk materials (metals, semiconductors, insulators).
• Amorphous. Liquids.

Methodology

• DFT, GW, BSE, TDDFT, Tight Binding, etc.
• Codes: abinit, exc, yambo, quantum espresso, cpmd, fhi96, octopus, dp

How to use ETSF services?

• Introduction Package for New Users.

Beamline Coordinator

Dr. Olivia Pulci

University of Rome Tor Vergata, Rome, Italy
Olivia [dot] Pulci [at] roma2 [dot] infn [dot] it

References

• Ab Initio Calculation of Excitonic Effects in the Optical Spectra of Semiconductors,
  S. Albrecht, L. Reining, R. Del Sole, and G. Onida, Phys. Rev. Lett. 80, 4510 (1998).
• Excitonic Effects in Solids Described by Time-Dependent Density-Functional Theory ,
  L. Reining, V. Olevano, A. Rubio, G. Onida, Phys. Rev. Lett. 88, 066404 (2002).
• Strain influence on valence-band ordering and excitons in ZnO: an ab-initio study ,
  A. Schleife, C. Rödl, F. fuchs, J. Furthmüller, F. Bechstedt, Appl. Phys. Lett. 91, 241915 (2007).
• Reflectance Anisotropy Spectra of the diamond (100) 2x1 surface: evidence of strongly bound surface-state excitons ,
  M. Palummo, O. Pulci, R. Del Sole, A. Marini, M. Schwitters, S. R. Haines, K. H. Williams, D. S. Martin, P. Weightman, J. E. Butler, Phys. Rev. Lett. 94, 087404 (2005).
• Excitons in Silicon Nanocrystallites: the Nature of Luminescence,
  E. Luppi, F. Iori, R. Magri, O. Pulci, R. Del Sole, S. Ossicini, E. Degoli, V. Olevano, Phys. Rev. B 75, 033303 (2007).
• Excitation Energies and Radiative Lifetimes of Ge_1-xSi_x Nanocrystals: Alloying Versus Confinement Effects,
  H.-Ch. Weissker, J. Furthmüller, and F. Bechstedt, Phys. Rev. Lett. 90, 085501 (2003).
• Ab initio calculations of many-body effects in liquids: the electronic excitations of water,
  V. Garbuio, M. Cascella, L. Reining, R. Del Sole, and O. Pulci, Phys. Rev. Lett. 97, 137402 (2006).
• Excitons in Boron Nitride Nanotubes: Dimensionality Effects,
  Ludger Wirtz, Andrea Marini, and Angel Rubio, Phys. Rev. Lett. 96, 126104 (2006).
• Second-harmonic polarizability including electron-hole attraction from bandstructure theory ,
  R. Leitsmann, W.G. Schmidt, P.H. Hahn, F. Bechstedt, Phys. Rev. B 71, 195209 (2005).
• Origin of the Optical Contrast in Phase-Change Materials ,
  Wojciech Welnic, Silvana Botti, Lucia Reining, and Matthias Wuttig, Phys. Rev. Lett. 98, 236403 (2007).

Energy Loss Spectroscopy

Beamline ELS is mainly dedicated towards studying, describing and predicting energy loss spectroscopies, such as Electron Energy Loss (EELS) and inelastic x-ray scattering (IXS).

EELS and IXS are two very different (electron microscope for EELS; synchrotron radiation for IXS) and yet complementary experimental techniques, in many respects. Energy, momentum, and spatial resolution are different for the two techniques, for instance. However, both EELS and IXS measure the same quantity, the dynamical structure factor $S(\mathbf{q},\omega)$. This quantity is related to the inverse dielectric function $ \varepsilon^{-1}(\mathbf{q},\omega)$, which is the quantity that is actually calculated via ab initio techniques, such as TDDFT or BSE.

What do we calculate?

• Electron Energy Loss Spectroscopy (EELS).
• Reflection Electron Energy Loss Spectroscopy (REELS).
• Inelastic and Coherent X-ray Scattering (IXRS,CIXS).

Which systems do we study?

• Bulk, Surfaces and Nanostructures.

Methodology

• Density functional approach: DFT-KS, TDDFT.
• Many-body techniques: Bethe-Salpeter Equation.
• Codes: DP, EXC, Yambo.

How to use ETSF services?

• Introduction Package for New Users.

Beamline Coordinator

Dr. Francesco Sottile

Ecole Polytechnique, Palaiseau, France
francesco [dot] sottile [at] polytechnique [dot] edu

References

• Excitonic Effects on the Silicon Plasmon Resonance ,
  V. Olevano and L. Reining, Phys. Rev. Lett. 86, 5962 (2001).
• Ab initio calculation of many-body effects on the EEL spectrum of the C(100) surface,
  Maurizia Palummo, Olivia Pulci, Andrea Marini, Lucia Reining, and Rodolfo Del Sole, Phys. Rev. B 74, 235431 (2006).
• Signatures of Short-Range Many-Body Effects in the Dielectric Function of Silicon for Finite Momentum Transfer ,
  Hans-Christian Weissker, Jorge Serrano, Simo Huotari, Fabien Bruneval, Francesco Sottile, Giulio Monaco, Michael Krisch, Valerio Olevano, and Lucia Reining, Phys. Rev. Lett. 97, 237602 (2006).
• Adsorption of molecular oxygen on GaAs(001) studied using high-resolution electron energy-loss spectroscopy,
  E. Placidi, C. Hogan, F. Arciprete, M. Fanfoni, F. Patella, R. Del Sole, and A. Balzarotti, Phys. Rev. B 73, 205345 (2006).

Quantum Transport

What do we calculate?

• Quantum Transport,Conductance and/or I-V curves of molecular and atomic junctions.
• Transients, memory effects, bound states, electromigration.
• STM, STS.

Which systems do we study?

• Metals, organic chains, atomic chains, carbon nanotubes.

Methodology

• Tight binding, classical nuclear dynamics.
• DFT (plane waves, Wannier), TDDFT.
• Many-body techniques: GW, Non-equilibrium Green's Function (NEGF).

How to use ETSF services?

• Introduction Package for New Users.

Beamline Coordinator

Dr. Peter Bokes

Slovak University of Technology, Bratislava, Slovakia
peter [dot] bokes [at] stuba [dot] sk

References

• Ab initio correlation effects on the electronic and transport properties of metal(II)-phthalocyanine-based devices,
  A. Calzolari, A. Ferretti, and M. Buongiorno Nardelli, Nanotechnology 18, 424013 (2007).
• Analysis of a dinitro-based molecular device,
  J.M. Seminario, A.G. Zacarias, and P.A. Derosa, J. Chem. Phys. 116, 1671 (2002).
• Nonequilibrium GW approach to quantum transport in nano-scale contacts ,
  K.S. Thygesen and A. Rubio , 126, 91101 (2007).
• First-Principles conductance of nanoscale junctions from the polarizability of finite systems,
  Matthieu J. Verstraete, P. Bokes, and R. W. Godby, J. Chem. Phys. 130, 124715 (2009).
• Time-dependent partition-free approach in resonant tunneling systems,
  G. Stefanucci, C.-O Almbladh, Phys. Rev. B 69, 195318 (2004).
• Time-dependent quantum transport: A practical scheme using density functional theory,
  S. Kurth, G. Stefanucci, C.-O Almbladh, A. Rubio, E.K.U. Gross, Phys. Rev. B 72, 035308 (2005).
• Classical Nuclear Motion in Quantum Transport ,
  C. Verdozzi, G. Stefanucci, C.-O Almbladh, Phys. Rev. Lett. 97, 046603 (2006).

Time Resolved Spectroscopy

Time-resolved spectroscopy is the name given to a set of experimental tools that allow for the measurement of time-resolved quantities. A frequently used technique is pump-probe spectroscopies where a very short laser pulse is used to excite the system, and then another pulse is used to "read" the excited-state. Common examples are the study of photo-induced chemical reactions, time-resolved infra-red or fluorescence spectroscopy.

In this Beamline we will deal not only with this kind of experiment, but with others in what may be defined as "time-dependent theoretical spectroscopies". By this we mean all quantities that can not be calculated by making straightforward use of the linear-response formalism in frequency space, either because the processes are inherently timedependent, as in time-resolved spectroscopy, or because we are dealing with processes that involve strong interactions between the probe and the system. Examples of the latter are (strongly) nonlinear optics, attosecond dynamics, ionisation yields, high-harmonic generation, and quantumcontrol of electronic/ionic processes.

What do we calculate?

• Time-resolved excitations, photoinduced chemical reactions, time-resolved fluorescence spectroscopy.
• Strongly non-linear optics, attosecond dynamics, ionization yields, high-harmonic generation.
• Quantum-control of electronic/ionic processes.

Which systems do we study?

• Molecules and Clusters.

Methodolody

• Time Dependent Density Functional Theory.
• Code: Octopus.

How to use ETSF services?

• Introduction Package for New Users.

Beamline Coordinator

Dr. Alberto Castro

Instituto de Biocomputación y Física de Sistemas Complejos (BIFI), Zaragoza
acastro [at] bifi [dot] es

References

• Time-dependent electron localization function,
  T. Burnus, M.A.L. Marques, and E.K.U. Gross, Phys. Rev. A R71, 10501 (2005).
• Excited states dynamics in time-dependent density functional theory: high-field molecular dissociation and harmonic generation,
  A. Castro, M.A.L. Marques, J.A. Alonso, G.F. Bertsch, and A. Rubio, Eur. Phys. J. D 28, 211 (2004).
• Optimal laser control of double quantum dots,
  E. Räsänen, A. Castro, J. Werschnik, A. Rubio and E. K. U. Gross, Phys. Rev. B 77, 085324 (2008).
• Control of Quantum Rings by Terahertz Laser Pulses,
  E. Räsänen, A. Castro, J. Werschnik, A. Rubio and E. K. U. Gross, Phys. Rev. Lett. 98, 157404 (2007).
• Strong-field ionization dynamics of a model H-2 molecule,
  M. Lein, T. Kreibich, E.K.U. Gross and V. Engel, Phys. Rev. A 65, 033403 (2002).

Photoemission Spectroscopy

Photoemission Spectroscopy (also known as Photoelectron Spectroscopy, PES) probes the energy levels of electrons, or more in general, the nature of chemical bonding and electron motion in a substance. PES is based on the Photoelectric Effect, which means that when light impinging on a surface is absorbed it induces the emission of electrons. Together with the related Auger spectroscopy, the PES technique is commonly referred as Electron Spectroscopy for Chemical Analysis (ESCA) and was pioneered by Swedish physicist Kai Siegbahn.

Basic Features of PES

The electronic transitions are selected by tuning the energy of the incident radiation (a). The electrons bring information via the Kinetic Energy, the direction of the momentum (the angle between the impinging radiation and emitted electrons, and their angle with the surface) and spin (b). The basic relation is $E_k=h\nu-\Phi-E_b$, with $\Phi$ the work function, $\nu$ the light frequency, and $E_b$ the binding energy. Photoelectrons suffer elastic/inelastic scattering when leaving the sample. The escape depth in solids is only few Ångström. This sometimes makes it problematic to separate surface and bulk contributions. In an atom excited by X rays, the main structures in the spectrum are due to photoelectrons. There are however also other peaks, of similar width but different energy, unrelated to incident photons, due to Auger recombination (c). In a proper theoretical formulation, PES and the Auger recombination should be treated on equal footing as a single coherent process.

In a theory of energy and angle resolved photoemission, a basic quantity of interest is the spectral function $A(q,E)=-\frac{1}{\pi}\frac{Im \Sigma(q,E)}{[E-\epsilon_q-Re\Sigma(q,E)]^2+Im\Sigma(q,E)^2}$, where $\epsilon_q$ is the one-body part and $\Sigma(q,E)$ accounts for the self-energy corrections. The quantity $A(q,E)$, to be compared to experimental PES spectra, is computed at the ab-initio level, and incorporates the information about the electronic energy bands, about the effects of correlation between electrons, the structure of the Fermi surface, the role of lattice vibrations (and in a more general form) about spin ordering.

Light sources

Traditional radiation sources are X-ray (XPS) and ultraviolet radiation (UPS). The use of synchrotron radiation has made such division somewhat conventional. In synchrotron sources the photon energy can be chosen continuously over a wide energy range. Other qualities of synchrotron light are high brightness and intensity, tunable polarization, the feasibility of short time-scale, time-resolved experiments.

Photoemission and the ETSF

What do we calculate?

• Reliable quasiparticle energies and band-gaps.
• Core and valence photoemission, angle resolved photoemission, thermal effects and electron-phonon coupling.
• Photoemission beyond the sudden approximation, lifetimes of electrons and holes, dependence of spectra on photon energy, spectral functions.
• Auger spectra.
• Scientific Highlights

Which systems do we study?

• Metals, semiconductors, molecules, surfaces, nanosystems, including e.g. transition metals and their alloys, transition-metal oxides, graphite, etc.

Methodology

• Density functional theory.
• Many-body techniques: GW, T-matrix-approximation.

How to use ETSF services?

• Introduction Package for New Users.

Beamline Coordinator

Dr. Claudio Verdozzi

Lund University, Lund, Sweden
Claudio [dot] Verdozzi [at] teorfys [dot] lu [dot] se

References

• Selectivity of Auger Decays to the Local Surface Environment
  M. I. Trioni, S. Caravati, G.P. Brivio, L. Floreano, F. Bruno, A. Morgante, Phys. Rev. Lett. 93, 206802 (2004). Scientific Highlight
• Exchange and Correlation Effects in Electronic Excitations of Cu2O
  F. Bruneval, N. Vast, L. Reining, M. Izquierdo, F. Sirotti, N. Barrett, Phys. Rev. Lett. 97, 267601 (2006). Scientific Highlight
• Electron-Electron Correlation in Graphite: A Combined Angle-Resolved Photoemission and First-Principles Study
  A. Grüneis, C. Attaccalite, T. Pichler, V. Zabolotnyy, H. Shiozawa, S. L. Molodtsov, D. Inosov, A. Koitzsch, M. Knupfer, J. Schiessling, R. Follath, R. Weber, P. Rudolf, L. Wirtz, and A. Rubio, Phys. Rev. Lett. 100, 037601 (2008). Scientific Highlight
• Jahn-Teller Spectral Fingerprint in Molecular Photoemission: C₆₀
  N. Manini,P. Gattari, P. E. Tosatti, Phys. Rev. Lett. 91, 196402 (2003). Scientific Highlight
• Photoemission beyond the sudden approximation
  C.-O. Almbladh, J. Phys.: Conf. Ser. 35, 127 (2006).

X-Ray Spectroscopy

The x-ray spectroscopy (XRS) aims to develop theoretical techniques for quantitative calculations of the various core-level spectroscopies measured at modern x-ray synchrotron facilities. These include x-ray absorption spectra (XAS), i.e., x-ray absorption fine structure (XAFS) and x-ray absorption near edge structure (XANES), and related spectra such as x-ray magnetic circular dichroism (XMCD), which are widely used to understand structural, vibrational and magnetic properties ofmaterials.

The primary engine for these calculations is the FEFF code. This approach uses a Real-space Green's function (RSGF) approach that builds in many-body effects such as inelastic losses, core-hole screening, and Debye-Waller factors [1,2] . Additional many body effects are treated with TDDFT, BSE, and spectral functions [2] . The RSGF approach in FEFF can also calculate core-level x-ray scattering factors (including diffraction anomalous spectra), x-ray emission spectra (XES), non-resonant X-ray Raman scattering (XRS) and core-level electron energy loss spectra (EELS) and various optical constants from the UV-x-ray energies. The approach is generally applicable to aperiodic systems throughout the periodic table, including bulk, surfaces, nano-structures, liquids, biostructures and other disordered materials as illustrated, e.g., in [3,4].

[1] J. J. Rehr and R. C. Albers, Rev. Mod. Phys. 72, 621 (2000).
[2] John J. Rehr et al., Comptes Rendus de Physique 10, 548 (2009).
[3] John J. Rehr et al., Phys. Chem. Chem. Phys. 1 2, 5503 (2010).
[4] Veronesi et al., Phys. Rev. B 82, 0201 01 (2010).

What do we calculate?

• Core level X-ray absorption spectra (XAS): X-ray absorption fine structure (XAFS), X-ray absorption near edge structure (XANES), and X-ray magnetic circular dichroism (XMCD).
• X-ray scattering factors, X-ray emission spectra, non-resonant X-ray Raman scattering (XRS) and electron energy loss spectra (EELS).

Which systems do we study?

• Bulk, Surfaces and Nanostructures. Liquids.

Methodology

• Real-space Green's function (RSGF) approaches including quasi-particle effects (GW), core-hole screening, and Debye-Waller factors.
• Additional many body effects treated with TDDFT, BSE, and spectral functions.

How to use ETSF services?

• Introduction Package for New Users.

Beamline Coordinator

Prof. John Rehr

University of Washington, Seattle, USA
jjr [at] phys [dot] washington [dot] edu

References

• Theoretical approaches to x-ray absorption fine structure ,
  J. J. Rehr and R. C. Albers, Rev. Mod. Phys. 72, 621 (2000).
• Theory and calculations of X-ray spectra: XAS, XES, XRS, and NRIXS ,
  J.J. Rehr, Radiation Physics and Chemistry 75, 1547 (2006).
• FEFF Project.

Vibrational Spectroscopy

“..everything that living things do can be understood in terms of the jigglings and wigglings of atoms..” [R. P. Feynmann, in "Six Easy Pieces" (Addison-Wesley, Reading MA), p. 59. (1991)]

This beamline is dedicated to vibrational spectroscopy, such as Infrared absorption and Raman scattering. These two experimental techniques allow to determine the vibrational properties  of matter (phonons in solids or molecular vibrations, typically in the 100-5000 cm^-1 range) by analyzing its interaction with light: absorption and scattering of photons

In Infrared spectroscopy, infrared light over a broad frequencies is passed through a sample. The matter absorbs the light only for some specific frequencies corresponding to the vibrational modes of the system and which fulfil some selection rules (the IR-active modes). Hence, for these frequencies, the light is attenuated when it passes through the sample. By measuring the intensity of the transmitted light at each frequency, the IR-active modes can be determined.

In Raman spectroscopy, a sample is illuminated with a monochromatic light (usually a laser beam in the visible, near infrared, or near ultraviolet range). The light interacts (inelastic or Raman scattering) with some specific vibrational modes of the system, which fulfil selection rules that are complementary to IR spectroscopy (Raman-active modes). As a result, the energy of the laser photons (and hence, the frequency of the light) may be shifted up or down by amounts corresponding to the various energies of the vibrational modes of the system.

What do we calculate?

• Infrared absorption: IR frequencies and intensities.
• Raman scattering: Raman frequencies and intensities.

Which systems do we study?

• Bulk, Surfaces and Nanostructures.

Methodology

• Density Functional Perturbation Theory (DFPT).

How to use ETSF services?

• Introduction Package for New Users.

Beamline Coordinator

Prof. Gian-Marco Rignanese

Université Catholique de Louvain, Louvain-la-Neuve, Belgium
gian-marco [dot] rignanese [at] uclouvain [dot] be

References

• Phonons and related crystal properties from density-functional perturbation theory,
  S. Baroni, S. de Gironcoli, A. Dal Corso, and P. Giannozzi, Rev. Mod. Phys. <>73, 515 (2001).
• Green-function approach to linear response in solids,
  S. Baroni, P. Giannozzi, and A. Testa, Phys. Rev. Lett. 58, 1861 (1987).
• Density-functional approach to nonlinear-response coefficients of solids,
  X. Gonze and J.-P. Vigneron, Phys. Rev. B 39, 13120 (1989).
• Dynamical matrices, born effective charges, dielectric permittivity tensors, and interatomic force constants from density-functional perturbation theory,
  X. Gonze and C. Lee, Phys. Rev. B 55, 10355 (1997).
• Nonlinear optical susceptibilities, raman efficiencies, and electro-optic tensors from first-principles density functional perturbation theory,
  M. Veithen, X. Gonze, and Ph. Ghosez, Phys. Rev. B 71, 125107 (1997).
• First-principle studies of the lattice dynamics of crystals, and related properties,
  X. Gonze, G.-M. Rignanese, and R. Caracas, Z. Krist 220, 458 (2005).