Dresden 2009 – wissenschaftliches Programm
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MA: Fachverband Magnetismus
MA 13: Poster Ia: Electron Theory (1); Magnetic Imaging (2,3); Thin Films (4-25); MSMA (26-33); Magn. Semiconductors (34-42); Magn. Half Metals and Oxides (43-60)
MA 13.1: Poster
Dienstag, 24. März 2009, 10:15–13:00, P1A
Exact thermodynamics of the extended Hubbard model for a cubic cluster — •David Zwicker and Rolf Schumann — Institute for Theoretical Physics, TU Dresden, Dresden D-01062, Germany
The Hubbard model extended by nearest-neighbor Coulomb and Heisenberg exchange interaction for an eight-site cubic cluster is studied by means of an exact diagonalization using all known interaction parameter-independent symmetries. The ground state plots in dependendence of the model parameters for the complete parameter space show a multitude of ground state crossings for all occupation numbers. We determine the ground state phase diagram in dependence of the chemical potential µ, hence describing the cubic cluster gas. Within the standard Hubbard model, we find 2-4 and 6-8 degeneration points (DPs) for a wide parameter region, i.e. steps in n(µ) higher than one. These DPs can be destroyed by applying a magnetic field h or a very high correlation energy U. The critical field hcrit in dependence on U is calculated. Furthermore, the influence of the additional interactions onto the thermodynamic properties is studied.