Self-doping effect on the Mott transition accompanied with threefold charge ordering in (DCNQI)2Cu

The commensurate state with threefold lattice distortion in the insulating phase of (DCNQI)2Cu is studied based on a two-band Peierls–Hubbard model by using the density-matrix renormalization-group method. With strong electron correlation among the d electrons, self-consistent lattice modulation strongly blocks the charge transfer between the π and d orbitals in order to keep the commensurability condition even when the π–d level difference is widely varied. A transition to an incommensurate phase requires a large deviation of the π–d level difference from the optimal case.