Variational study on missing bond-charge repulsion on the extended Hubbard model: Effects on polyacetylene

The variational approach is applied to the study on the effect of Coulomb interaction between electrons on the dimerization in a one-dimensional commensurability-two Peierls system, such as trans-polyacetylene. For the case of omitting direct repulsion between electrons in the bonds between sites W, it is confirmed that the weak interactions tend to enhance the dimerization; but when W is included, this enhancement will be attenuated. If \W\ is sufficiently large, the net effect of electron-electron interactions will reduce the magnitude of the electron-phonon-induced dimerization.