Doctoral Dissertations

Date of Award

5-2001

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Physics

Major Professor

Adolfo G. Eguiluz

Committee Members

Gerald D. Mahan, Robert N. Compton, Bennett C. Larson

Abstract

Two different but complementary quantum mechanical many-body problems are investigated. These problems include both static and dynamic aspects of the electronelectron interaction in real materials. In Chapter One, we take up the cases of Ag and Ni with a microscopic evaluation of the dielectric function and loss function using the formalism of time dependent density functional theory and all-electron techniques. We address the striking line shapes that have been recently observed via inelastic scattering experiments. The present work reveals three relevant energy scales for excitations in the selected systems. These scales are argued to be generic to a large number of 3d and 4d metals, and include the threshold for excitation of d electrons, final state energies, and the plasmon energy. Our results for Ag corroborate the experimental interpretation of the anomalous dispersion of the nominal plasmon loss, and shed new light on the striking line shape as well as predicting an anomalous dispersion of the nominal plasmon lifetime. In agreement with experiment, the theoretical loss spectrum of Ni is found to be equally complex with two prominent loss features at ~22eV and ~28 eV. The ab initio results demonstrate that both phase space and a strong modulation of d → p transitions lead to the predicted behavior. Moreover, in contrast to the canonical description that has been used to describe these features, we find them to be quite different from plasma oscillations. In Chapter Two, we address static properties of the electron-electron interaction as it pertains to ground state properties. In the exchange-only method one approximates the exchange-correlation energy functional of density functional theory by its Hartree-Fock form, ensuring that the method adheres to several scaling laws and identities which are violated by the local density and generalized gradient approximations. Although there is no formal correspondence to eigenvalue gaps determined by photoemission or inverse photoemission, we find that exchange-only results partially remove the discrepancy between these energy gaps and those obtained based on the local density approximation. However, we also find marked discrepancies with other recent theoretical treatments. Suggestions for future research are made.

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