Dresden 2006 – scientific programme

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TT: Tiefe Temperaturen

TT 19: Correlated Electrons: Low-dimensional Materials

TT 19.18: Talk

Tuesday, March 28, 2006, 18:30–18:45, HSZ 301

Coulomb parameters and spectral function for TTF-TCNQ — •Erik Koch — Institut für Festkörperforschung, Forschungszentrum Jülich, D-52425 Jülich

The key ingredient for a realistic description of strongly correlated materials by a model Hamiltonian is the reliable determination of the Coulomb repulsion parameters. For molecular crystals this is possible. For the example of the quasi one-dimensional organic conductor TTF-TCNQ we show how to calculate the Coulomb repulsion energies between charges in the HOMO/LUMO orbitals. As these molecules, like most π-systems, are planar, we find that a description by a standard Hubbard model with only on-site interaction U is not sufficient. Instead, interactions between charges on different molecules have to be taken into account. Including these longer range interactions has a strong effect on the spectral function, giving results consistent with the photoemission data, without having to assume unrealistically large band-width, as is necessary when when neglecting the Coulomb terms between neighboring molecules.