We study the one-dimensional extended Hubbard model with alternating size of the hopping integrals using the density-matrix renormalization group method. We calculate the spin gap, the Tomonaga-Luttinger parameter, and the charge-density-wave order parameter for various dimerizations, interaction strengths, and band fillings. At half band-filling the spin and charge excitations are gapped but these gaps disappear for infinitesimal hole doping. At quarter filling, the umklapp scattering in the half-filled lower Peierls band generates a gap for the charge excitations but the gapless spin excitations can be described in terms of an effective antiferromagnetic Heisenberg model. Beyond a critical strength for the nearest-neighbor interaction, the dimerized extended Hubbard model at quarter filling develops a charge-density-wave ground state. The dimerization and the nearest-neighbor Coulomb interaction strongly reduce the Tomonaga-Luttinger parameter from its value for the bare Hubbard model. We discuss the relevance of our findings for the Bechgaard salts.We study the one-dimensional extended Hubbard model with alternating size of the hopping integrals using the density-matrix renormalization group method. We calculate the spin gap, the Tomonaga-Luttinger parameter, and the charge-density-wave order parameter for various dimerizations, interaction strengths, and band fillings. At half band-filling the spin and charge excitations are gapped but these gaps disappear for infinitesimal hole doping. At quarter filling, the umklapp scattering in the half-filled lower Peierls band generates a gap for the charge excitations but the gapless spin excitations can be described in terms of an effective antiferromagnetic Heisenberg model. Beyond a critical strength for the nearest-neighbor interaction, the dimerized extended Hubbard model at quarter filling develops a charge-density-wave ground state. The dimerization and the nearest-neighbor Coulomb interaction strongly reduce the Tomonaga-Luttinger parameter from its value for the bare Hubbard model. We discuss the relevance of our findings for the Bechgaard salts.

arXiv:cond-mat/0605433Physical Review BDec 14, 200621 citations

Spectrum of the Fermi-Linearized Extended Hubbard Model on a Dimer

L. R. Evangelista, Arianna Montorsi, Mario Rasetti

NATO ASI series. Series B : PhysicsJan 1, 19910 citations

Modeling electron-electron interactions in reduced-dimensional materials: Bond-charge Coulomb repulsion and dimerization in Peierls-Hubbard models

D. K. Campbell, J. Tinka Gammel, Eugene Loh

To the conventional Peierls-Hubbard model, involving both on-site (U) and nearest-neighbor (V) Coulomb repulsions, we add ``off-diagonal'' terms, not expressible purely in terms of site densities, representing bond-bond (W) and mixed bond-site (X) electron-electron repulsive interactions involving nearest neighbors. We review earlier analyses of these interactions and discuss relative magnitudes of the parameters in applications to real materials. As a specific illustration, we investigate the effects of the off-diagonal W and X terms on dimerization in the one-dimensional, half-filled-band Peierls-Hubbard models, which have been widely applied to conjugated polymers (such as trans-polyacetylene) and to related quasi-one-dimensional charge-density wave (CDW) systems. Using both weak- and strong-coupling perturbation theory for large systems and exact diagonalizations of small systems, we investigate thoroughly the nature of the ground state of the model. For a broad range of the site-diagonal Hubbard parameters (U,V), including the values believed to be relevant to trans-polyacetylene, we find that the off-diagonal terms (W,X) initially enhance dimerization, thereby stabilizing the dimerized [or bond-order-wave (BOW)] ground state. For (unphysically) large values of W relative to U and V, dimerization is destroyed, and the BOW ground state goes over to a ferromagnetic ground state or a CDW ground state, depending on the relative sizes of U, V, and W. We conclude with a general discussion of the applicability of the Peierls-Hubbard models to quasi-one-dimensional materials, including the potential importance of the breaking of charge conjugation (``particle-hole'') symmetry by the X term.To the conventional Peierls-Hubbard model, involving both on-site (U) and nearest-neighbor (V) Coulomb repulsions, we add ``off-diagonal'' terms, not expressible purely in terms of site densities, representing bond-bond (W) and mixed bond-site (X) electron-electron repulsive interactions involving nearest neighbors. We review earlier analyses of these interactions and discuss relative magnitudes of the parameters in applications to real materials. As a specific illustration, we investigate the effects of the off-diagonal W and X terms on dimerization in the one-dimensional, half-filled-band Peierls-Hubbard models, which have been widely applied to conjugated polymers (such as trans-polyacetylene) and to related quasi-one-dimensional charge-density wave (CDW) systems. Using both weak- and strong-coupling perturbation theory for large systems and exact diagonalizations of small systems, we investigate thoroughly the nature of the ground state of the model. For a broad range of the site-diagonal Hubbard parameters (U,V), including the values believed to be relevant to trans-polyacetylene, we find that the off-diagonal terms (W,X) initially enhance dimerization, thereby stabilizing the dimerized [or bond-order-wave (BOW)] ground state. For (unphysically) large values of W relative to U and V, dimerization is destroyed, and the BOW ground state goes over to a ferromagnetic ground state or a CDW ground state, depending on the relative sizes of U, V, and W. We conclude with a general discussion of the applicability of the Peierls-Hubbard models to quasi-one-dimensional materials, including the potential importance of the breaking of charge conjugation (``particle-hole'') symmetry by the X term.

Physical review. B, Condensed matterJul 1, 1990132 citations

Bond-charge coulomb repulsion in peierls-hubbard models

David K Campbell, J. Tinka Gammel, Eugene Loh

We investigate the general applicability of the standard Peierls-Hubbard model, involving both on-site ( $U$ ) and nearest-neighbor ( $V$ ) Coulomb repulsions, by adding nearest-neighbor off-diagonal terms representing the bond ( $W$ ) and mixed bond-site ( $X$ ) electron-electron repulsive interactions. For a broad range of the site-diagonal Hubbard parameters ( $U,V$ ), we find that the off-diagonal terms ( $W,X$ ) initially enhance dimerization, thereby stabilizing the dimerized ground state.We investigate the general applicability of the standard Peierls-Hubbard model, involving both on-site ($U$) and nearest-neighbor ($V$) Coulomb repulsions, by adding nearest-neighbor off-diagonal terms representing the bond ($W$) and mixed bond-site ($X$) electron-electron repulsive interactions. For a broad range of the site-diagonal Hubbard parameters ($U,V$), we find that the off-diagonal terms ($W,X$) initially enhance dimerization, thereby stabilizing the dimerized ground state.

Physical review. B, Condensed matterDec 1, 198860 citations

SPECTRUM OF THE FERMI-LINEARIZED EXTENDED HUBBARD-MODEL ON A DIMER

L. R. EVANGELISTA, RASETTI M., Arianna Montorsi

Jan 1, 19920 citations

We investigate the general applicability of the standard Peierls-Hubbard model, involving both on-site (

U

) and nearest-neighbor (

V

) Coulomb repulsions, by adding nearest-neighbor off-diagonal terms representing the bond (

W

) and mixed bond-site (

X

) electron-electron repulsive interactions. For a broad range of the site-diagonal Hubbard parameters (

U,V

), we find that the off-diagonal terms (

W,X

) initially enhance dimerization, thereby stabilizing the dimerized ground state.