MOTT-PEIERLS TRANSITION IN THE EXTENDED PEIERLS-HUBBARD MODEL

The one-dimensional extended Peierls-Hubbard model is studied at several band fillings using the densitymatrix renormalization-group method. Results show that the ground state evolves from a Mott-Peierls insulator, with a correlation gap at half-filling, to a soliton lattice with a small band gap away from half-filling. It is also confirmed that the ground state of the Peierls-Hubbard model undergoes a transition to a metallic state at finite doping. These results show that electronic correlation effects should be taken into account in theoretical studies of doped polyacetylene. They also show that a Mott-Peierls theory could explain the insulator-metal transition observed in this material. @S0163-1829~98!06716-2# Since the discovery of the metallic phase of doped polyacetylene, this material has been extensively studied, 1,2 but the mechanism of the insulator-metal transition observed upon doping is still poorly understood. It is known that both the Peierls instability and electronic correlations play a fundamental role in the formation and properties of the insulating phase, 3 and thus undoped polyacetylene is a Mott-Peierls insulator. 4 Therefore, ten years ago, Baeriswyl, Carmelo, and Maki 5 proposed that the insulator-metal transition was also driven by the interplay of electron-electron and electronphonon interactions. Within the restricted Hartree-Fock approximation, they showed the possibility of such a MottPeierls insulator-metal transition in the Peierls-Hubbard model, which is the simplest model of polyacetylene including both interactions. Recently, several works using sophisticated numerical many-body methods, such as the Gutzwiller variational wave function 6 and quantum Monte Carlo ~QMC! simulations, 7 have confirmed the occurrence of