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TT: Fachverband Tiefe Temperaturen

TT 20: Correlated Electrons - Poster Session

TT 20.57: Poster

Wednesday, March 28, 2007, 14:00–17:45, Poster A

Realistic description of TTF-TCNQ using massively parallel exact diagonalization — •Andreas Dolfen and Erik Koch — Institut für Festkörperforschung, Forschungszentrum Jülich, Germany

The photoemission spectrum of the quasi one-dimensional organic metal TTF-TCNQ can be described qualitatively using a t-U Hubbard model. For such calculations we have developed a parallel Lanczos code which runs efficiently on modern massively parallel supercomputers like JUBL, Jülich’s new BlueGene/L system. To overcome the limitations of the finite system-size we employ cluster perturbation theory (CPT), giving us access to the angular-resolved spectral function with high resolution. As a result, we can resolve the spin-charge separation. Moreover, we compute the total energy of the system by using the Galitskii-Migdal theorem.

Experiments and theoretical estimates for TTF-TCNQ suggest a value for the hopping parameter t. The parameter needed to fit the experiment is, however, larger by a factor of two. We resolve this problem by including realistic values for the next-neighbor interaction V into the model. The effect of this longer-range Coulomb interaction is to broaden the spectrum – very similar to increasing the value of t. This explains why the ad-hoc doubling of t yields a good comparison with experiment. Moreover, we find that the effect of V can be understood already in first-order perturbation theory.