Sökning: "many-body approximations"

Hittade 5 uppsatser innehållade orden many-body approximations.

  1. 1. Green's Functions Investigations in Quantum Transport Geometries

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

    Författare :Philip Johansson; [2022]
    Nyckelord :Quantum transport; Green s functions; self-energy; non-equilibrium; many-body physics; Physics and Astronomy;

    Sammanfattning : In this thesis we employ the non-equilibrium Green’s function (NEGF) method to study both finite and infinite systems. We develop a codebase capable of computing the steady state interacting NEGF in open systems, i.e. LÄS MER

  3. 2. Variational approach to the many-body problem with error estimation

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

    Författare :Claes Rogius Svensson; [2018]
    Nyckelord :Many-body problems; Slater determinants; variational approach; Physics and Astronomy;

    Sammanfattning : In this thesis a method for doing approximate calculations of the ground state of quantum mechanical many-body systems is developed and implemented. This method uses the Hartree-Fock method as a starting point and approximates the ground state as a linear combination of non-orthogonal Slater determinants. LÄS MER

  4. 3. Excited States in Variational Many-Body Approaches

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

    Författare :David Gustafsson; [2018]
    Nyckelord :quantum mechanics; many-body problems; excited states; Hartree-Fock method; variational method; VAMPIR; Physics and Astronomy;

    Sammanfattning : A method is implemented wherein numerical approximations to the ground and first few excited states of a quantum mechanical N -body 1D harmonic oscillator are found through variational methods, representing the states as a linear combination of normalized pseudo-states which are themselves linear combinations of non-orthogonal Slater determinants. These states are then used as a low energy basis for configuration interaction. LÄS MER

  5. 4. Many-body-based DFT treatment of fermions in optical lattices

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

    Författare :Jérémie Westergren; [2017]
    Nyckelord :DFT; density functional theory; MBA; many-body approximations; Hubbard model; Ultra cold atoms; cold atoms; optical lattice; Physics and Astronomy;

    Sammanfattning : With recent advances in the field of ultra cold atoms one can, by trapping atoms at low temperatures by laser beams, simulate systems which can be adequately described by single-band lattice Hamiltonians. Also, due to the high parameter tunability of the experimental setups, lattice disorder can be introduced in a con- trolled fashion in these systems. LÄS MER

  7. 5. A mean-field approach to attractive few-body Fermi gas

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

    Författare :Morten Piibeleht; [2016]
    Nyckelord :HFB; hartree-fock-bogoliubov; fermi gas; higgs mode; QRPA; quasiparticles; random phase approximation; Physics and Astronomy;

    Sammanfattning : Quantum many-body systems can be studied theoretically from first principles using microscopic models, but the computational cost of numerically exact calculations increases exponentially with the number of particles and the complexity of the interaction, limiting the systems that can be analysed. The Hartree-Fock-Bogoliubov (HFB) and quasiparticle random phase approximation (QRPA) methods, heavily used in nuclear physics, rely on mean-field approximations but scale more favourably with increasing system size and complexity. LÄS MER