Electron-hole excitations and optical spectra of rare gas solids

Abstract

This thesis is a theoretical study of the optical and dielectric properties of semiconductors and insulators. The quantity that defines the relationship between measurable optical properties and electronic structure of materials is the macroscopic dielectric function εαβ(q, ω) . The aim of this thesis is accurate calculation and interpretation of the longitudinal dielectric function by highly reliable ab initio techniques. In order to achieve this, two types of excitations of an electronic system are relevant: single-particle excitations and electron-hole excitations. The key concept in our approach is to describe these excitations with the corresponding one- and two-particle Green's functions. A recently developed approach, which combines three computational techniques, was employed in the study. Firstly, density functional and Hartree-Fock methods were used in ground state calculations to generate non-interacting single-particle Green's functions. In the second step, single-particle excitations were studied using the G W approximation to the electron self-energy operator. Finally, the electron-hole interaction was calculated and a Bethe-Salpeter equation solved, leading to coupled electron-hole excitations. This approach allows bound exciton states to be studied and entire optical spectra calculated. In addition, the influence of local field effects and single-particle excitations was examined separately. The importance of including both single-particle and electron-hole excitations in calculations of the dielectric function is highlighted.