Sökning: "Hubbard I Approximation"

Hittade 4 uppsatser innehållade orden Hubbard I Approximation.

1. 1. Machine-Learning for Lattice Models in and out of Equilibrium

   Master-uppsats, Lunds universitet/Matematisk fysik; Lunds universitet/Fysiska institutionen

   Författare :Johannes Sandberg; [2021]
   Nyckelord :Physics and Astronomy;

   Sammanfattning : Machine-learning methods have in recent years seen a great deal of use in condensed matter physics. In this thesis we apply such methods, specifically machine-learning with artificial neural networks, to the equilibrium and non-equilibrium description of the Hubbard and Hubbard-Holstein models. LÄS MER

3. 2. Ensemble Green's Function Theory for Interacting Electrons with Degenerate Ground States

   Master-uppsats, Lunds universitet/Matematisk fysik; Lunds universitet/Fysiska institutionen

   Författare :Erik Linnér; [2019]
   Nyckelord :Green s function; Degeneracy; Density matrix; Ensemble; GW; Zero-temperature; Finite-temperature; Hubbard model; Two-dimensional harmonic oscillator; Ising model; Hydrogen-like model; Physics and Astronomy;

   Sammanfattning : An ensemble Green's function theory for many-electron systems with degenerate ground states, based on the von Neumann density matrix formalism, is proposed. The formalism is constructed without an assumption of an adiabatic connection. An ensemble analogue of Hedin's equations and the GW Approximation (GWA) is constructed. LÄS MER

4. 3. Combining the GW Approximation with the Hubbard I Approximation for strongly correlated materials

   Magister-uppsats, Lunds universitet/Matematisk fysik; Lunds universitet/Fysiska institutionen

   Författare :Torsten Strunck; [2019]
   Nyckelord :GWA; GW Approximation; HIA; Hubbard I Approximation; Hubbard-I Approximation; Hubbard model; DMFT; Dynamical Mean Field Theory; strongly correlated materials; electron correlations; solid state physics; Physics and Astronomy;

   Sammanfattning : In this thesis, the GW approximation (GWA, Green's function G times screened interaction W) and the Hubbard I approximation (HIA) are combined in a non-self-consistent one-shot calculation to determine the electronic structure of a one-dimensional strongly-correlated model. The scheme was chosen to incorporate both screening effects through the GWA and strong on-site correlations through the atomic HIA. LÄS MER

5. 4. Near-local density approximation approach to one-dimensional lattice systems

   Kandidat-uppsats, Lunds universitet/Matematisk fysik; Lunds universitet/Fysiska institutionen

   Författare :Basheer Joudeh; [2018]
   Nyckelord :DFT; Hartree; Hartree-Fock; LDA; BALDA; Mean-field; Hubbard; SOFT; Physics and Astronomy;

   Sammanfattning : Describing many-body quantum systems has been an analytically and computationally challenging task since the advent of quantum mechanics. However, in the past 50 years as a result of our technological advancement and the emergence of methods such as density-functional theory (DFT), we have taken crucial steps forward regarding our ability to study and understand large quantum systems. LÄS MER