Search for dissertations about: "GW-approximation"
Showing result 1 - 5 of 10 swedish dissertations containing the word GW-approximation.
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1. Model Vertices Beyond the GW Approximation
Abstract : 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. READ MORE
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2. Self-consistency and the GW-approximation
Abstract : 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 $GWA$. READ MORE
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3. Static and Dynamic Correlation Effects in Atoms
Abstract : The thesis considers the effects of electron correlation by studying the two opposite limits of atoms in the ground state and atoms in strong laser pulses. Computational methods and theoretical approaches differ significantly due to the different physical processes that are studied in these two cases. READ MORE
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4. Unifying first-principles and model approaches for strongly correlated materials : Interplay between long- and short-range correlations
Abstract : 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. READ MORE
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5. First principles methods for electronic structure calculations of solids
Abstract : A straightforward gradient expansion of the exchange energy of a perturbed electron gas is performed. Studied perturbations range from very weak to those that produce, e.g., a silicon-like band structure with a band gap. READ MORE
