Data di Pubblicazione:
2008
Citazione:
Ab initio approach to density response and excitation spectra in metallic systems / M. Cazzaniga ; G. Onida, N. Manini, L. G. A. Molinari. DIPARTIMENTO DI FISICA, 2008 Dec 22. 21. ciclo, Anno Accademico 2008/2009. [10.13130/cazzaniga-marco_phd2008-12-22].
Abstract:
In this thesis I propose a detailed discussion of the calculation of the dielectric
response of metallic systems. We mainly performed simulations of Al and Na, since
their near free-electron like behaviour permits also a comparison with the results of
the HEG model. On the other hand, we also explored the possibility that our methods
could be applied to more complex system. In this direction we performed calculation
of the optical properties of ferromagnetic Fe, which includes the additional complexity
of the presence of the 3d electrons. We also tried to understand if the accuracy of ab
initio calculations in the case of semiconductors can be extended to metallic systems.
The present thesis focuses on the frequency-dependent dielectric function є(q,ω).
In the first part of this thesis we review briefly the GW and TDDFT approaches used
in our calculations. We will also motivate the study of bulk metals. In the second
part of this thesis the new methods developed in this work do deal with the intraband
contributions will be described. We will finally analyze the obtained results.
In the discussion of the GW calculations for metals, we propose a method to deal
with the intraband term based on a fit of the finite-momentum screened interaction.
This methods works efficiently when the plasmon pole approximation is an accurate
assumption.
In addition to optical adsorption, other experiments permit to access the dielectric
properties of metals, including the energy-loss spectroscopy and inelastic X-ray scattering
spectroscopy (IXSS). In the present thesis we performed a systematic calculation of
the dynamic structure factor of Na and Al to understand the role of electronic correlation
beyond the random phase approximation (RPA).We perform TDDFT simulations
using several exchange and correlation kernels and including quasiparticle effects, to
understand how they are important to provide a satisfactory theoretical description of
the experimental measurements. TDDFT is not only able to predict loss function measurements,
but also optical properties. This thesis address also that problem proposing
a new method to deal with the intraband transitions, method applied to Al chosen as
benchmark and to ferromagnetic Fe.
In Chapter 1 we introduce the many-body problem, which is described in detail in
Chapter 2, where we review the many-body perturbation theory and the GW approximation.
In Chapter 3 the TDDFT and the linear response formalism are presented.
We introduce the dielectric function and briefly discuss its main features in Chapter
4. In Chapter 5 we show the applications, by presenting the problem of the fictitious gap introduced by the GW corrections and by proposing a fit on the polarizability to
deal with the intraband transitions. We apply finally TDDFT, by discussing the IXSS
spectra of Na and of Al in Chapter 6. Optical properties are discussed in Chapter 7.
Tipologia IRIS:
13 - Tesi di dottorato discussa entro ottobre 2010
Elenco autori:
M. Cazzaniga
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