Extended Peierls-Hubbard Model for One-Dimensional N-Sites N-Electrons System. I. Phase Diagram by Mean Field Theory

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Abstract
The phase diagram of a one-dimensional many-electron system with site-diagonal electron-phonon(e-p) coupling and short-ranged inter-site electron-electron(e-e) repulsion as well as intra-site one is studied within the mean field theory for electrons and in the adiabatic limit for phonons. The theory covers the whole region of four parameters characterizing the system: the transfer energy of electron T , the e-p coupling energy S , the intra- and inter-site e-e repulsive enegies U and V , and the phase diagram is given in a tetrahedral coordinate space spanned by T , U , S and V . It is proved that the “ T - U - S - V tetrahedron” is divided into SDW and CDW regions by the interface U = S +2 V , that is, “ S ” competes with “ U ” but cooperates with “ V ”. The “ S ↔ U ” and “ S ↔ T ” competitions appeared in the energy gap of CDW can explain the experimental results of halogen-bridged mixed-valence metal complexs.