A MODEL FOR THE ELECTRONIC-STRUCTURES OF BETA-(BEDT-TTF)(2)X AND KAPPA-(BEDT-TTF)(2)X

A simple microscopic model is obtained for beta and kappa-(BEDT-TTF)(2 )X starting from the PPP model with hyperconjugation of BEDT-TTF. UHF calculations for clusters with intramolecular. electron Coulomb intera ction show that only HOMOs are important in the crystals and for most value of the screened electron Coulomb interaction in the HOMO, U, the systems can be represented by dimers consisting of Hubbard type units . The dimers arrange in triangular lattices. The gap in a dimer is sma ll but the electron correlation measured by U/t is very strong. Copyri ght (C) 1996 Elsevier Science Ltd