A Valence-Bond/Hartree–Fock method to determine the Hubbard transfer integrals in organic conductors Original Research Article

In previous reports [F. Castet, A. Fritsch, L. Ducasse, J. Phys. (Paris) I, 6 (1996) 583; L. Ducasse, A. Fritsch, F. Castet, Synth. Metals 85 (1997) 1627], we presented a new mixed Valence-Bond/Hartree–Fock (VB/HF) method to extract the Extended Hubbard Coulombic parameters in organic conductors. In our approach, calculations (restricted to all valence electrons) are performed on finite size clusters using crystal data and molecular orbitals (MOs) localised on fragments. The optimized MOs depend on the charge of the fragment. The present paper describes the calculation scheme for matrix elements between distinct Valence-Bond configurations involved in charge transfer processes, i.e. the transfer integrals. Calculations were performed for different representative salts with either quasi one-dimensional or two-dimensional character, using different semi-empirical hamiltonians.