Exact diagonalization study on the extended Hubbard model in an anisotropic triangular lattice

A half-filled-band extended Hubbard model on an anisotropic triangular lattice is studied, using an exact diagonalization method, with kappa-(BEDT-TTF)(2)X in mind. In the isotropic case, the charge fluctuation of (27 pi/3, 2 pi/3) is enhanced by the introduction of off-site Coulomb interaction (V). In the case of V = 0, the anti ferromagnetic (AF) fluctuation is sizable for small frustration. However, when V is introduced, the AF fluctuation is rapidly suppressed and becomes substantially small, irrespective of the strength of frustration. Thus, it is revealed that both spin and charge fluctuations are sensitive to the shifts of t'/t and V/t. (C) 2008 Published by Elsevier Ltd.