Vous êtes ici Ecole Doctorale Sciences Ecole Doctorale Thématique MAIN Agenda UCL - M. Ginatomassi - Core electrons and self-consistency in the GW approximation from a PAW perspective

Aucun événement

Aucune offre d'emploi

Le Vendredi 29 Mai 2009 de 14h30 à 14h30

Invitation à la défense publique de thèse de Monsieur Matteo
GIANTOMASSI

Titre : Core electrons and self-consistency in the GW approximation from a PAW perspective

Résumé :

Density functional theory (DFT) performs reasonably well for the
determination of structural properties of many materials, but fails to
predict electronic band gap values accurately.

Such a failure of DFT is not unexpected, since there exists no formal
justification for interpreting the DFT eigenvalues as addition or
removal energies of the many-body system (quasiparticle energies).

An alternative approach to the study of exchange-correlation effects in
many-particle systems is provided by many-body perturbation theory
(MBPT), which defines a rigorous approach to description of
excited-state properties based on the Green's function formalism and
the concept of quasiparticle electrons. Within MBPT, one can calculate
the quasiparticle (QP) energies and the QP amplitudes by approximately
solving, within the so-called GW approximation, the set of coupled
integro-differential equations proposed by Hedin in 1965.

The GW method generally yields significantly better values for QP
energies with respect to DFT as it accounts for the dynamic many-body
effects in the electron-electron interaction going beyond the
mean-field approximation of independent Kohn-Sham particles. The
drawback of such an involved approach, however, is its large
computational cost, which is mainly due to the evaluation of dielectric
matrices, their inversion, and the solution of a non-Hermitian and
nonlinear eigenvalue problem.

The first part of this PhD research is devoted to the implementation of
an efficient and scalable coarse-grained parallel algorithms and the
development of state-of-the-art methods to solve the GW equations.

All these techniques are then applied to the study of the quasiparticle
band structures of SiO2 in the alpha quartz crystalline structure. The
effects of the different approximations involved in the theory, the
influence of self-consistency, and a systematic analysis of the
reliability of the different plasmon-pole models are presented and
discussed.

The second part of this PhD work is dedicated to the implementation of
a methodological approach to the solution of the GW equations based on
the so-called projector augmented wave method (PAW) proposed by Blochl
in 1994. This new approach permits to remove many of the limitations
intrinsic to the use of the pseudopotential technique widely used for
ab-initio calculations, allowing one to reach GW results closer to an
all-electron implementation while still maintaining computational
efficiency, and flexibility. This allows us to achieve a coherent
implementation of many different algorithms which enables a detailed
comparison of GW calculations not yet performed until now. Results for
the quasiparticle band structure and optical spectra of prototype s-
and p-compounds are discussed and compared to recent studies reported
in the scientific literature (when available).

La soutenance
aura lieu le vendredi 29 mai 2009

Vendredi 29 mai 2009 à 14h30

Auditoire BARB93

Place Sainte-Barbe

Louvain-la-Neuve

Accès Louvain-la-Neuve Biéreau

Dernière mise à jour par EDT MAIN Vendredi 22 Mai 2009