Les Deuxièmes Journées Théorie à SOLEIL

Les Deuxièmes Journées
Théorie à SOLEIL
8 – 10 Novembre 2016
Programme
Abstracts
Registration
Programme
Mardi 8 Novembre 9hr00-11hr00
Delphine Cabaret (IMPMC): Introduction au calcul de structure électronique par DFT ;
Application à la spectroscopie d’absorption des rayons X.
Break - Posters
Mardi 8 Novembre 11hr30 - 13hr00
Matteo Gatti, Francesco Sottile and Lucia Reining (ETSF): Theoretical
spectroscopy : methods and applications in the collaborations between the ETSF and
SOLEIL.
Lunch
Mardi 8 Novembre 14hr30-16hr30 / Break (posters) / 17hr00 - 18hr30
Nadejda Bouldi and Guillaume Radtke (IMPMC): XSpectra, A tool for X-ray absorption
spectra (XAS) calculations.
_______ End of the day _________
Mercredi 9 Novembre 9hr-10hr30 / Break (posters) / 11hr00-13hr00
Marie-Anne Arrio and Amélie Juhin: Multiplet et dichroïsme circulaire.
Lunch
Mercredi 9 Novembre 14hr30 – 16hr00 / Break (posters) / 16hr30-18hr00
Keith Gilmore (ESRF): OCEAN, An implementation of the Bethe-Salpeter equation for
calculating core and valence level spectra.
________ End of the day ________
Jeudi 10 Novembre 9hr00-10hr30 / Break (posters) / 11hr00-12hr30
Yannick Dappe (CNRS/CEA-IRAMIS): Density Functional Theory for Nanostructures:
the Fireball code in localized orbitals basis set and its applications.
________ End of the day ________
Introduction au calcul de structure électronique
par DFT : Application à la spectroscopie d’absorption
des rayons X
par Delphine Cabaret (IMPMC)
Institut de Minéralogie, de Physique des Matériaux, et de Cosmochimie (IMPMC), Sorbonne Universités – UPMC Univ Paris 06,
UMR CNRS 7590, Muséum National d’Histoire Naturelle, IRD UMR 206, 4 place Jussieu, F-75005 Paris, France
Ce cours, comme le suggère son intitulé, comportera deux parties.
La première partie sera consacrée au calcul de la structure électronique d’un système
constitué d’un ensemble d’électrons et de noyaux par la théorie de la fonctionnelle de la
densité (DFT). Les différentes approximations sous-jacentes à la mise en œuvre de
cette théorie seront présentées. La DFT sera ainsi resituée dans un cadre plus large des
théories basées sur l’approximation de champ moyen. Un focus sur les méthodes
utilisant une base d’ondes plane et des conditions aux limites périodiques sera effectué
(comme c’est le cas dans la suite de codes Quantum-ESPRESSO).
La deuxième partie portera sur les calculs de spectres d’absorption des rayons X. Nous
verrons dans quels cas (type de seuils, transitions électroniques) les spectres peuvent
être calculés grâce à la DFT et comment le calcul de la structure électronique intervient
dans la détermination de la section efficace, et ce afin d’introduire le tutorial XSpectra.
Theoretical spectroscopy : methods and applications
in the collaborations between the ETSF and SOLEIL
Par Matteo Gatti, Francesco Sottile and Lucia Reining
Theoretical Spectroscopy Group LSI - CNRS Ecole Polytechnique, 91128 Palaiseau, France
Synchrotron SOLEIL, L’Orme des Merisiers, 91190 Saint Aubin, France
In this tutorial we will present the ab initio theoretical approaches and computational
codes that are developed by the scientists of the European Theoretical Spectroscopy
Facility (ETSF) (see http://www.etsf.eu). The focus will be on fundamental ideas,
possibilities and limitations of the theories and codes that are currently used to
complement experiments by providing tools of analysis and new predictions.
Methods for electronic excitations based on density functionals and Green's functions
will be reviewed together with the ETSF codes that implement those methods (see
http://www.etsf.eu/resources/software). Typical applications will be illustrated with an
emphasis on the fruitful interactions between theory and experiments that are performed
at SOLEIL.
XSpectra
A tool for X-ray absorption spectra (XAS) calculations
Par Nadejda Bouldi1,2 et Guillaume Radtke1
1
Institut de Minéralogie, de Physique des Matériaux, et de Cosmochimie (IMPMC), Sorbonne Universités – UPMC Univ Paris 06,
UMR CNRS 7590, Muséum National d’Histoire Naturelle, IRD UMR 206, 4 place Jussieu, F-75005 Paris, France
2
Synchrotron SOLEIL, L’Orme des Merisiers, 91190 Saint Aubin, France
In this tutorial, we give a hands-on introduction to XSpectra [1], a module for
calculating X-ray absorption spectra distributed in the DFT based Quantum ESPRESSO
[2] package. XSpectra calculates X-ray absorption dipolar and quadrupolar crosssections in the pre-edge to near-edge region of K- and L-edges, within the single particle
approximation and based on a continued fraction approach [3].
The basic theoretical concepts required for a comprehensive use of the code will
be reviewed and systematically illustrated through a series of examples. In particular,
the effect of the core-hole on the fine structure, the use of supercells and the calculation
of dichroic signal will be illustrated in the case of the Si-K edge in SiO2 whereas the
calculation of quadrupolar contributions will be demonstrated through the example of the
Ni-K edge in NiO. School attendees will participate to practical exercises including (i) the
generation of GIPAW pseudopotentials including a core-hole; (ii) the construction and
self-consistent calculation of supercells containing an excited absorbing atom and (iii)
the XAS calculation with XSpectra with a special emphasis on the description of input
parameters related to the Lanczos method and continued fraction calculation.
References
[1] C. Gougoussis, M. Calandra, A. P. Seitsonen and F. Mauri, Phys. Rev. B 80, 075102
(2009)
[2] P. Giannozzi et al., J. Phys. Condens. Matter 21, 395502 (2009).
[3] M. Taillefumier, D. Cabaret, A. M. Flank and F. Mauri, Phys. Rev. B 66, 195107
(2002)
Multiplet et dichroïsme circulaire
Par Marie-Anne Arrio et Amélie Juhin
Institut de Minéralogie, de Physique des Matériaux, et de Cosmochimie (IMPMC), Sorbonne Universités – UPMC Univ Paris 06,
UMR CNRS 7590, Muséum National d’Histoire Naturelle, IRD UMR 206, 4 place Jussieu, F-75005 Paris, France
La théorie des multiplets (LFM : Ligand field multiplet theory) repose sur un
modèle atomistique basé sur Hartree-Fock.1,2 L’ion et tous ses électrons sont traités et
décrits à l’aide de fonctions multiélectroniques. La structure locale de l’ion est introduite
par un terme de champ cristallin ou champ de ligand. Dans le cas d’un ion magnétique,
un terme Zeeman est ajouté. En spectroscopie de cœur, le modèle LFM s’applique dans
le cas où il existe de forte répulsion électronique dans le niveau excité et entre les
électrons du niveau de cœur et du niveau excité. C’est le cas des seuils L2,3 des ions de
transition (3d et 4d) et les seuils M4,5 des ions terre-rare. Nous verrons que le modèle
LFM peut aussi être utilisé dans le calcul des pré-seuils K des éléments de transition 3d.
Les calculs permettent, entre autre, d’avoir des informations sur : le degré d’oxydation,
la symétrie locale, la covalence de la liaison chimique, les moments de spin, d’orbite
dans le cas d’ion magnétique.
Nous présenterons succinctement les bases de la théorie LFM et nous montrerons
l’utilisation de quelques programmes : TTMULT, CTM4XAS et QUANTY.
1. de Groot, Frank; Kotani, Akio ; Core Level Spectroscopy of Solids Introduction ;
Book Series: Advances in Condensed Matter Science ; vol 6 (2008)
2. van der Laan, Gerrit in « Magnetism: A Synchrotron Radiation Approach »,
chapter 7 ; Editors: Beaurepaire, E., Bulou, H., Scheurer, F., Kappler, J.P. (Eds.)
OCEAN
An implementation of the Bethe-Salpeter equation for
calculating core and valence level spectra.
Par Keith Gilmore
European Synchrotron Radiation Facility, 71 avenue des Martyrs, 38000 Grenoble, France
Core-hole density functional theory and atomic multiplet theory are two common
approaches to calculating X-ray spectra. Atomic multiplets have the advantages of
being easy to use and fast. However, this approach is typically limited to a local
description of the electronic structure and often includes parameter freedom. The corehole DFT method can rigorously account for band-structure and accurately reproduce
the near-edge spectra involving s-orbital core levels. However, this approach often fails
when the core-hole has non-zero angular momentum. This is fundamentally a limitation
of the underlying independent particle approximation.
The simplest step beyond the independent particle approximation is to include the
interaction between the core-hole and the excited electron. This is usually formulated as
a Bethe-Salpeter equation (BSE) that includes single particle terms for the energy levels
of the core-hole and excited electron, and an interaction between the electron and hole.
This two-particle description of the many-body final state is already a significant
improvement over the independent particle approximation and yields favorable
agreement with experiment even for previously challenging edges. The BSE code
OCEAN1 (Obtaining Core Excitations using ab initio electronic structures and the NIST
BSE solver) can generate x-ray absorption (XAS), emission (XES), and both resonant
and non-resonant inelastic x-ray scattering (N/RIXS) spectra for a variety of systems.
As examples, we have previously calculated spectra of ionic crystals (LiF), wide- and
narrow-gap semiconductors (SrTiO3, PbSe), metals (3d transition metals), amorphous
solids (SiO2), liquids (H2O), and molecules (various). The ability to calculate XMCD will
be implemented shortly. Valence excitations may also be calculated.
This tutorial will cover the basic theoretical aspects of the Bethe-Salpeter method
before continuing with a practical session. The exercises for participants will include
various examples to illustrate basic x-ray absorption calculations at K- and L-edges, xray emission, and non-resonant inelastic x-ray scattering. A more involved final example
will demonstrate the generation of a direct RIXS map.
[1] K. Gilmore et al., Comp. Phys. Comm. 197, 109 (2015).
Density Functional Theory for Nanostructures:
the Fireball code in localized orbitals basis set and its
applications
Par Yannick Dappe
CEA-Saclay, IRAMIS, SPCSI, F-91191 Gif-sur-Yvette, France
In this presentation, I will recall some basic concepts of Density Functional
Theory (DFT), in particular in the frame of localized orbital basis set considering the
occupation number as a variable instead of the usual spatial electronic density. In that
manner, I will present some specificities of the Fireball code, like the implementation of a
perturbation theory to treat van der Waals (vdW) interactions, and some other
advantages of this code. Comparison will also be presented with tight-binding or
molecular dynamics methods.
In a second part, I will present some applications of the Fireball code, in
collaboration with experimental groups and synchrotron characterizations. I will therefore
present several examples on electronic structure modifications of graphene and
bidimensional materials like doping or gap opening, based on bandstructure and Density
of States (DOS) calculations. More on structural aspects, I will also discuss some
examples on molecular adsorption on surface or molecular self-assembling, using vdW
optimization between the molecules. Description of molecular electronic structures will
also be presented for perspectives in STM images or electronic transport calculations.
Registration
The registration is free of charge.
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[email protected]
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