The Hubbard Model for One-Dimensional Solids
In recent years several unambiguous experimental evidences have been found stressing the relevance of electron-electron (e-e) interaction in one-dimensional (1D) solids, either charge-transfer salts1 or polymers.2 However there is not agreement between physicists on how to model e-e interaction in polymers, so that the effects of such interaction on the dimerization amplitude and on the band gap are still controversial.3–13 The Hubbard model14 has been generally adopted to investigate the role of e-e interaction in 1D solids. It is the solid state counterpart of the Pariser-Parr-Pople (PPP) model, widely tested and successfully applied in molecular physics. However, the electrons in isolated molecules experience an unscreened Coulomb repulsion, whereas in 1D solids the interaction between the electrons along a chain may be screened due to the presence of mobile electrons on neighboring chains. The applicability of Hubbard model to systems with highly screened potential still has to be settled.
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- 21.The large absolute values of X, W, Y and X’ terms in the S≳ 0.75 regime are due to the vanishing of U in this regime, where the S expansion is clearly unphysical. Moreover in evaluating X’ we have always retained the S’ terms, even if they should be neglected for S≳ 0.25. The results are not qualitatively modified.Google Scholar