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Screened T-matrix theory for strongly correlated materials

par Pina Romaniello - 15 octobre 2014

Toutes les versions de cet article : English , français

PhD advisor : Pina Romaniello

Financial support : not determined

Strongly correlated electron systems exhibit remarkable electronic and magnetic properties, such as metal-insulator transitions, half-metallicity, or unconventional superconductivity, which make them among the most attractive and versatile materials. Typically these materials have incompletely filled d- or f-electron shells with narrow energy bands. In this case a theoretical description requires an accurate treatment of electron correlation. This represents one of the greatest challenges in condensed-matter physics today.

One of the most popular approaches in condensed-matter physics is many-body perturbation theory (MBPT) based on Green’s functions [1]. Within the so called GW approximation to electron correlation, MBPT has become, over the last two decades, the tool of choice for the calculations of quasiparticle (QP) band structures and direct and inverse photo emission spectra of many materials improving substantially over the results provided by static mean-field electronic structure methods. However GW suffers from some fundamental shortcomings, and, in particular, it is not expected to describe strong correlation.

In this project we propose to look at an approximation to electron correlation which goes beyond GW : a screened version of the T matrix approximation [2]. We will first explore this approximation on exactly solvable model systems, such as Hubbard chains, and we will then implement it (or an improved version, if needed) in the open source code Abinit ( for calculations on real materials.

This project is also connected to a collaborative project, which involves many researchers in Europe within the framework of the European Theoretical Spectroscopy Facility (ETSF ). The goal is to share knowledge for progressing together in the comprehension and description of electron correlation.

It is thus preferable that the candidate for this project has good communication skills, a good level of English, the pleasure for calculations << pencil and paper >>, with a solid background in mathematics, and computer skills.

[1] A. L. Fetter and J. D. Walecka, Quantum Theory of Many-Particle Systems (New York : Dover, 2003)

[2] P. Romaniello, F. Bechstedt, and L. Reining, Phys. Rev. B 85, 155131 (2012)

Contact : Pina Romaniello, Chargée de recherche CNRS, Laboratoire de Physique Théorique

e-mail :, Phone : +33 (0)5 61 55 75 74