Organisers

• Francesco Sottile (Ecole Polytechnique, France)
• Xavier Gonze (Universite Catholique de Louvain, Belgium)
• Gian-Marco Rignanese (Université Catholique de Louvain, Belgium)
• Valerio Olevano (CNRS Institut Neel, Grenoble, France)

Supports

   CECAM

   ESF-Intelbiomat

European theoretical Spectroscopy Facility

Description

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Electronic excitations are probed by experimental techniques such as optical absorption, EELS and photo-emission (direct or inverse). From the theory point of view, excitations and excited state properties are out of the reach of density-functional theory (DFT), which is a ground-state theory. In the last twenty years other ab-initio theories and frameworks, which are able to describe electronic excitations and spectroscopy, have become more and more used: time-dependent density-functional theory (TDDFT) and many-body perturbation theory (MBPT) or Green's function theory (GW approximation and Bethe-Salpeter equation BSE). In fact, computational solutions and codes have been developed in order to implement these theories and to provide tools to calculate excited state properties.The present school focuses on these points, covering theoretical, practical, and also numerical aspects of TDDFT and MBPT, and codes implementing them (ABINIT, DP, EXC).

Scientific Objectives

In the basis of our previous experience with the organisation of schools (see Spectroscopy Lectures and ABINIT Summer School), the presentation of the theory will be followed by practical classes and hands-on tutorials. At the end of the school, students will have sufficient working knowledge to pursue their projects at their home institution. The participants are expected to have a fair knowledge of DFT prior to the school (see Ref. 1) and to be familiar with one plane-wave pseudopotential based software. Indeed, although at the beginning of the school, we will make sure that the DFT level of all participants is enough in this respect and provide the needed complementary information and training, the purpose of the school is to go beyond DFT, with hands-on exercices based on plane-wave implementations.

Beside the organisers, who will care about most of the theoretical lectures, other tutors are invited to come, namely Valerie Veniard (DR-CNRS), Silvana Botti (CR-CNRS), Fabien Bruneval (CEA) and a couple of post-docs deeply involved in the development of the codes (and so ideally placed to guarantee the hands-on as well as to talk about the practical side of the codes).

<h2>Plan of lectures</h2>
Day 1
- Introduction to Spectroscopy (Theory - 1/2 h)
- Density Functional Theory (Theory - 2 h)
- Microscopic-Macroscopic connection (Theory - 1 h)
- DFT with Abinit (hands-on - 3 h)

Day 2
- Time Dependent DFT (Theory - 2 h)
- TDDFT - Casida eqs. (Theory - 1 h)
- TDDFT with DP (hands-on - 3 h)

Day 3
- Brief round table (1/2 h)
- Introduction to Many-Body Perturbation Theory (Theory - 1 h)
- Many Body Perturbation Theory: GW approximation (Theory - 1.5 h)
- Discussion session (2-3 h)

Day 4
- MBPT and GW in practice (Theory - 1.5 h)
- GW with Abinit (hands-on - 4 h)

Day 5
- Bethe-Salpeter Equation (Theory - 1 h)
- BSE vs TDDFT (Theory - 1 h)
- BSE with EXC (hands-on - 3 h)

References

[1] R. M. Martin Electronic structure : Basic Theory and Practical Methods, Cambridge University Press (2004)

[2] F. Aryasetiawan and O. Gunnarsson The GW method, Rep. Prog. Phys. 61 237 (1998)

[3] G.Onida, L. Reining and A. Rubio. Electronic excitations: density-functional versus many-body Green's function approaches, Rev. Mod. Phys. 74 601 (2002)

[4] Strinati, Riv. Nuovo Cim. 11, 1 (1988)