Regensburg 2000 – scientific programme

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TT: Tiefe Temperaturen

TT 17: Postersitzung II: Pinning und Vortexdynamik (1-8), Supraleitung: Theorie (9-13), Korrelierte Elektronen (14-48), Niederdimensionale Systeme (49-68), Quantenflüssigkeiten (69-75)

TT 17.42: Poster

Wednesday, March 29, 2000, 14:30–18:00, A

The Hubbard Model for Small Clusters: Comparison of Exact and Approximate Results — •Silvio Francisco, AAmir Massoud Sawadkouhi, and Gerd Czycholl — Institut f"ur Theoretische Physik, Universit"at Bremen

We study the Hubbard model on a small finite cluster of N lattice sites. Using the symmetries and constants of motion (total electron number, spin, momentum ) all eigenvalues and eigenstates can be determined analytically up to N = 4. The exact result for the one- particle Green function and selfenergy can be obtained. These exact results for the ground state energy and the selfenergy are compared with relsults of standard approximations (Hartree- Fock, Gutzwiller ansatz, U- perturbation theory, FLEX ).