The ground-state property of one-dimensional extended Hubbard model is investigated at quarter filling. By using spin-charge factorized wave function in the U → ∞ limit, the effective exchange coupling Jeff and spin susceptibility χ are calculated as a function of nearest-neighbor Coulomb interaction V. It is found that Jeff is suppressed by the effect of V through charge fluctuation. The results indicate these quantities have no singularities at the transition point because of the Berezinskii-Kosterlitz-Thouless-type transition of charge ordering. We also confirm the results by exact diagonalization method in the realistic parameter range. The relevance to the experiments on quasi one-dimensional organic conductor ( DI-DCNQI )2 Ag is discussed.
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