Charge Transfer Instability with Structural Change. III. Effect of Fluctuation in One-Dimensional N-Sites N-Electrons System

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Abstract
The phase diagram for one-dimensional many-electron system with the electron-electron and electron-phonon interactions is studied within the RPA and in the adiabatic limit, so as to clarify the effect of the fluctuation on the phase diagram given by the mean field theory (MFT). The ground-state energy gain due to the virtual excitation of the bound and unbound electron-hole pairs is calculated. The newly obtained phase diagram is such that the SDW region erodes the CDW region given by the MFT. In the CDW, the lowest allowed excitation is a pair of charge transfer type excitons with the energy nearly equal to the gap, while in the SDW it is a pair of magnons just above the ground state. This difference results in the erosion, indicating that the comprehensive study of all excited states is essential in obtaining the ground state itself.