A Valence-Bond/Hartree-Fock method to determine the extended Hubbard parameters in organic conductors

The relative magnitude of the parameters describing the interaction between conduction electrons in organic conductors is not yet firmly established. A mixed Valence-Bond/Hartree-Fock method applied to all valence electrons calculations on finite size clusters was thus derived in order to size up the magnitude of the coulombic terms. An effective Hamiltonian built upon a single site orbital per molecule reproduces the whole set of VB energy levels. Coulombic parameters describing the interactions in clusters of organic molecules derived of TTF (tetrathiafulvalene) may be thus extracted. Intrachain and interchain terms for a series of quasi-1D and quasi-2D representative salts were evaluated. The magnitude of the coulombic terms (U ≅ 4 eV; V(nearest-neighbour) ≅ 2–3 eV) differs qualitatively from previous estimations and evidences the long range part of the potential.