Sökning: "GW approximation"
Visar resultat 1 - 5 av 15 avhandlingar innehållade orden GW approximation.
1. Model Vertices Beyond the GW Approximation
Sammanfattning : We study the effects of local vertex corrections to the self energy of the electron gas. We find that a vertex derived from time-dependent density-functional theory can give accurate self energies without including the explicit time dependence of the exchange-correlation potential provided, however, that a proper decay at large momentum transfer (large q) is built into the vertex function. LÄS MER
2. Unifying first-principles and model approaches for strongly correlated materials : Interplay between long- and short-range correlations
Sammanfattning : In materials with open 3$d$ and 4$f$ shells the valence electrons are relatively localized around the atoms which leads to large electron-electron correlations. These, so called strongly correlated materials, exhibit many intriguing properties such as high $T_c$ superconductivity, colossal magneto-resistance and heavy fermion behaviour. LÄS MER
3. Self-consistency and the GW-approximation
Sammanfattning : The effects of self-consistency in the GW-approximation are studied. The $GWA$ is known to describe the electronic properties of a wide range of materials very well. However, the calculations made so far have not taken into account the issue of self-consistency, which is implied in the original formulation of the $GWA$. LÄS MER
4. Periodized Thermal Greens Functions and Applications
Sammanfattning : This work describes a new formalism for Fermionic thermal Greens functions that are discretized in imaginary time. The discretization makes the thermal Greens function periodic in imaginary (Matsubara) frequency space and requires a generalisation of the Dyson equation and Luttinger-Ward-Baym-Kadanoff functional. LÄS MER
5. Electronic Structure and Optical Properties of Solar Energy Materials
Sammanfattning : In this thesis, we have studied the electronic and optical properties of solar energy m-terials. The studies are performed in the framework of density functional theory (DFT), GW, Bethe-Salpeter equation (BSE) approaches and Kinetic Monte Carlo (KMC). We present four sets of results. LÄS MER