Valerio Olevano

University of Grenoble, Grenoble, Rhône-Alpes, France

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Publications (75)243.96 Total impact

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    ABSTRACT: The effect of nanocrystal orientation on the energy loss spectra of monoclinic hafnia (m-HfO$_2$) is measured by high resolution transmission electron microscopy (HRTEM) and valence energy loss spectroscopy (VEELS) on high quality samples. For the same momentum-transfer directions, the dielectric properties are also calculated ab initio by time-dependent density-functional theory (TDDFT). Experiments and simulations evidence anisotropy in the dielectric properties of m-HfO$_2$, most notably with the direction-dependent oscillator strength of the main bulk plasmon. The anisotropic nature of m-HfO$_2$ may contribute to the differences among VEELS spectra reported in literature. The good agreement between the complex dielectric permittivity extracted from VEELS with nanometer spatial resolution, TDDFT modeling, and past literature demonstrates that the present HRTEM-VEELS device-oriented methodology is a possible solution to the difficult nanocharacterization challenges given in the International Technology Roadmap for Semiconductors.
    Applied Physics Letters 12/2014; 105(22):222904. DOI:10.1063/1.4903218 · 3.52 Impact Factor
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    ABSTRACT: A Comment on the Letter by M. Calandra and F. Mauri Phys. Rev. Lett. 106 196406 (2011) The authors of the Letter offer a Reply.
    Physical Review Letters 01/2014; 112(4):049701. DOI:10.1103/PhysRevLett.112.049701 · 7.73 Impact Factor
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    ABSTRACT: We review in this article recent developments within the framework of ab initio many-body perturbation theory aiming at providing an accurate description of the electronic and excitonic properties of pi-conjugated organic systems currently used in organic photovoltaic cells. In particular, techniques such as the GW and Bethe-Salpeter formalisms are being benchmarked for acenes, fullerenes, porphyrins, phthalocyanines, and other molecules of interest for solar energy applications. It is shown that not only the electronic properties, but also the electron-phonon coupling matrix elements, and the charge-transfer excitations in donor/acceptor complexes, are accurately described. The present calculations on molecules containing up to a hundred atoms are based on a recently developed Gaussian auxiliary basis implementation of the GW and Bethe-Salpeter formalism, including full dynamics with contour-deformation techniques, as implemented in the Fiesta code.
    Journal of Materials Science 11/2012; 47(21):7472-7481. DOI:10.1007/s10853-012-6401-7 · 2.31 Impact Factor
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    ABSTRACT: Within the framework of ab initio time-dependent density-functional theory (TD-DFT), we propose a static approximation to the exchange-correlation kernel based on the jellium-with-gap model. This kernel accounts for electron-hole interactions and it is able to address both strongly bound excitons and weak excitonic effects. TD-DFT absorption spectra of several bulk materials (both semiconductor and insulators) are reproduced in very good agreement with the experiments and with a low computational cost.
    Physical review. B, Condensed matter 10/2012; 87(20). DOI:10.1103/PhysRevB.87.205143 · 3.66 Impact Factor
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    ABSTRACT: We present two possible approaches to calculate the momentum distribution n(p) and the Compton profile within the framework of the ab initio GW approximation on the self-energy. The approaches are based on integration of the Green's function along either the real or the imaginary axes. Examples will be presented on the jellium model and on real bulk sodium. Advantages and drawbacks of both methods are discussed in comparison with accurate quantum Monte Carlo (QMC) calculations and x-ray Compton scattering experiments. We illustrate the effect of many-body correlations and disentangle them from band-structure and anisotropy effects by a comparison with density functional theory in the local density approximation. Our results suggest the use of G0W0 momentum distributions as reference for future experiments and theory developments.
    Physical review. B, Condensed matter 10/2012; 86(19). DOI:10.1103/PhysRevB.86.195123 · 3.66 Impact Factor
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    ABSTRACT: We present both theoretical ab-initio results within the Hedin's GW approximation and experimental angle-resolved photoemission and scanning tunneling spectroscopymeasurements on TiSe2. With respect to the density-functional Kohn-Sham metallic picture, the many-body GW self-energy leads to a approximate to 0.2- eV band-gap insulator consistent with our STS spectra at 5 K. The highest valence and the lowest conduction bands are strongly renormalized, with a loss of k(2) parabolic dispersion toward a k(4) shape. In particular, GW moves the top of valence moved toward a circle of points away from Gamma, arising in a Mexican hat shape commonly associated with an excitonic insulator. Our calculations are in good agreement with experiment.
    Physical Review B 05/2012; 85(19-19). DOI:10.1103/PhysRevB.85.195111 · 3.66 Impact Factor
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    ABSTRACT: The band structure of gold is calculated using ab initio many-body perturbation theory. Different approximations within the GW approach are considered. Standard single-shot G0W0 corrections modify the sp-like bands while leaving unchanged the 5d occupied bands. Beyond G0W0, quasiparticle self-consistency on the wave functions lowers the 5d bands. Globally, many-body effects achieve an opening of the 5d-6sp interband gap of ∼0.4 to ∼0.8 eV, reducing the discrepancy with the experiment. Finally, the quasiparticle band structure is compared to the one obtained by the widely used HSE (Heyd, Scuseria, and Ernzerhof) hybrid functional.
    Physical review. B, Condensed matter 03/2012; 86(12). DOI:10.1103/PhysRevB.86.125125 · 3.66 Impact Factor
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    ABSTRACT: Cited By (since 1996): 1, Export Date: 22 November 2012, Source: Scopus, Art. No.: 195111, CODEN: PRBMD, doi: 10.1103/PhysRevB.85.195111, Language of Original Document: English, Correspondence Address: Cazzaniga, M.; Università Degli Studi di Milano, Physics Department, Milano, Italy, References: Mott, N.F., (1961) Philos. Mag., 6, p. 287. , 1478-6435 10.1080/14786436108243318;
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    ABSTRACT: We calculate the off-diagonal density matrix of the homogeneous electron gas at zero temperature using unbiased reptation Monte Carlo calculations for various densities and extrapolate the momentum distribution and the kinetic and potential energies to the thermodynamic limit. Our results on the renormalization factor allow us to validate approximate G0W0 calculations concerning quasiparticle properties over a broad density region (1≤r(s)≲10) and show that, near the Fermi surface, vertex corrections and self-consistency aspects almost cancel each other out.
    Physical Review Letters 09/2011; 107(11):110402. DOI:10.1103/PhysRevLett.107.110402 · 7.73 Impact Factor
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    ABSTRACT: On the basis of first-principles GW calculations, we study the quasiparticle properties of the guanine, adenine, cytosine, thymine, and uracil DNA and RNA nucleobases. Beyond standard G0W0 calculations, starting from Kohn-Sham eigenstates obtained with (semi)local functionals, a simple self-consistency on the eigenvalues allows us to obtain vertical ionization energies and electron affinities within an average 0.11 and 0.18 eV error, respectively, as compared to state-of-the-art coupled-cluster and multiconfigurational perturbative quantum chemistry approaches. Further, GW calculations predict the correct π-character of the highest occupied state, due to several level crossings between density functional and GW calculations. Our study is based on a recent Gaussian-basis implementation of GW calculations with explicit treatment of dynamical screening through contour deformation techniques.
    Physical review. B, Condensed matter 03/2011; 83(11). DOI:10.1103/PhysRevB.83.115123 · 3.66 Impact Factor
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    ABSTRACT: We present both theoretical ab initio GW and experimental angle-resolved photoemission (ARPES) and scanning tunneling (STS) spectroscopy results on TiSe2. With respect to the density-functional Kohn-Sham metallic picture, the many-body GW self-energy leads to a ~ 0.2 eV band gap insulator consistent with our STS spectra at 5 K. The band shape is strongly renormalized, with the top-of-valence moved towards a circle of points away from \Gamma, arising in a mexican hat feature typical of an excitonic insulator. Our calculations are in good agreement with experiment.
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    ABSTRACT: The conductance of single molecule junctions is calculated using a Landauer approach combined to many-body perturbation theory MBPT) to account for electron correlation. The mere correction of the density-functional theory eigenvalues, which is the standard procedure for quasiparticle calculations within MBPT, is found not to affect noticeably the zero-bias conductance. To reduce it and so improve the agreement with the experiments, the wavefunctions also need to be updated by including the non-diagonal elements of the self-energy operator.
    Physical review. B, Condensed matter 02/2011; 84. DOI:10.1103/PhysRevB.84.045426 · 3.66 Impact Factor
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    X. Blase, C. Attaccalite, V. Olevano
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    ABSTRACT: We evaluate the performances of ab initio GW calculations for the ionization energies and highest occupied molecular orbital-lowest unoccupied molecular orbital gaps of 13 gas phase molecules of interest for organic electronic and photovoltaic applications, including the C60 fullerene, pentacene, free-base porphyrins and phtalocyanine, PTCDA, and standard monomers such as thiophene, fluorene, benzothiazole, or thiadiazole. Standard G0W0 calculations, that is, starting from eigenstates obtained with local or semilocal functionals, significantly improve the ionization energy and band gap as compared to density functional theory Kohn-Sham results, but the calculated quasiparticle values remain too small as a result of overscreening. Starting from Hartree-Fock-like eigenvalues provides much better results and is equivalent to performing self-consistency on the eigenvalues, with a resulting accuracy of 2%–4% as compared to experiment. Our calculations are based on an efficient Gaussian-basis implementation of GW with explicit treatment of the dynamical screening through contour deformation techniques.
    Physical review. B, Condensed matter 11/2010; 83(11). DOI:10.1103/PhysRevB.83.115103 · 3.66 Impact Factor
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    ABSTRACT: We investigate some aspects of the self-consistency in the Dyson-Schwinger approach to both the QED and the self-interacting scalar field theories. We prove that the set of the Dyson-Schwinger equations, together with the Green-Ward-Takahashi identity, is equivalent to the analogous set of integral equations studied in condensed matter, namely, many-body perturbation theory, where it is solved self-consistently and iteratively. In this framework, we compute the nonperturbative solution of the gap equation for the self-interacting scalar field theory.
    Physical review D: Particles and fields 11/2010; 82(9). DOI:10.1103/PhysRevD.82.094023
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    ABSTRACT: We present experimental and theoretical results on the momentum distribution and the quasiparticle renormalization factor in sodium. From an x-ray Compton-profile measurement of the valence-electron-momentum density, we derive its discontinuity at the Fermi wave vector. This yields an accurate measure of the renormalization factor that we compare with quantum Monte Carlo and G0W0 calculations performed both on crystalline sodium and on the homogeneous electron gas.
    Physical Review Letters 08/2010; 105(8):086403. DOI:10.1103/PhysRevLett.105.086403 · 7.73 Impact Factor
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    ABSTRACT: We present experimental inelastic x-ray scattering (IXS) and ab initio time-dependent density-functional-theory (TDDFT) studies of YBa2Cu3O7-delta . The response of the low-lying Ba5p and Y4p core electrons is shown to interact strongly with the Cu3d and O2p excitations, with important consequences on screening. The agreement between IXS and TDDFT results is excellent, apart from a new type of excitations, mainly related to loosely bound Ba electrons and significantly affected by correlations. This points to correlation mechanisms not fully described by TDDFT that might have a role in giving rise to antiscreening.
    Physical Review B 08/2010; 82(6):064514. DOI:10.1103/PhysRevB.82.064514 · 3.66 Impact Factor
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    ABSTRACT: We present experimental inelastic x-ray scattering (IXS) and ab initio time-dependent density-functional-theory (TDDFT) studies of YBa2Cu3O7−δ. The response of the low-lying Ba 5p and Y 4p core electrons is shown to interact strongly with the Cu 3d and O 2p excitations, with important consequences on screening. The agreement between IXS and TDDFT results is excellent, apart from a new type of excitations, mainly related to loosely bound Ba electrons and significantly affected by correlations. This points to correlation mechanisms not fully described by TDDFT that might have a role in giving rise to antiscreening.
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    Pierre Darancet, Valerio Olevano, Didier Mayou
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    ABSTRACT: We introduce a quantum transport formalism based on a map of a real three-dimensional lead-conductor-lead system into an effective one-dimensional (1D) system. The resulting effective 1D theory is an in principle exact formalism to calculate the conductance. Besides being more efficient than the principal layers approach, it naturally leads to a five-partitioned workbench (instead of three) where each part of the device (the true central device, the ballistic and the nonballistic leads) is explicitely treated, allowing better physical insight into the contact resistance mechanisms. Independently, we derive a generalized Fisher-Lee formula and a generalized Meir-Wingreen formula for the correlated and uncorrelated conductance and current of the system where the initial restrictions to ballistic leads are generalized to the case of resistive contacts. We present an application to graphene nanoribbons.
    Physical review. B, Condensed matter 04/2010; 81(15). DOI:10.1103/PhysRevB.81.155422 · 3.66 Impact Factor
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    ABSTRACT: We present ab initio many-body calculations of the optical absorption in bulk graphite, graphene and bilayer of graphene. Electron-hole interaction is included solving the Bethe-Salpeter equation on top of a GW quasiparticle electronic structure. For all three systems, we observe strong excitonic effects at high energy, well beyond the continuum of pi-->pi* transitions. In graphite, these affect the onset of sigma-->sigma* transitions. In graphene, we predict an excitonic resonance at 8.3 eV arising from a background continuum of dipole forbidden transitions. In the graphene bilayer, the resonance is shifted to 9.6 eV. Our results for graphite are in good agreement with experiments.
    Physical review. B, Condensed matter 03/2010; 81(12). DOI:10.1103/PhysRevB.81.121405 · 3.66 Impact Factor
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    Valerio Olevano, Massimo Ladisa
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    ABSTRACT: We present a relativistic covariant form of many-body theory. The many-body covariant Lagrangian is derived from QED by integrating out the internal non-quantized electromagnetic field. The ordinary many-body Hamiltonian is recovered as an approximation to the exact covariant theory that contains many-body terms beyond the solely electrostatic interaction, e.g. the Lorentz force among electrons, spin-spin etc. Spin and relativistic terms, e.g. spin-orbit, are also automatically accounted. Moreover, the theory is compact, gauge-invariant and respects causality. Comment: Secondary subj-class: hep-ph

Publication Stats

2k Citations
243.96 Total Impact Points

Institutions

  • 2014
    • University of Grenoble
      Grenoble, Rhône-Alpes, France
  • 2008–2014
    • Institut Néel
      Grenoble, Rhône-Alpes, France
    • École Polytechnique
      Paliseau, Île-de-France, France
  • 2005–2012
    • French National Centre for Scientific Research
      • Institut Néel
      Lutetia Parisorum, Île-de-France, France
  • 2008–2011
    • University Joseph Fourier - Grenoble 1
      • Institut Néel
      Grenoble, Rhone-Alpes, France
  • 1999–2005
    • University of Rome Tor Vergata
      • Dipartimento di Fisica
      Roma, Latium, Italy
  • 2004
    • Atomic Energy and Alternative Energies Commission
      Fontenay, Île-de-France, France