Effects of e-e Interaction on the CDW of MX Complex

We have considered the effects of Hubbard repulsion on the charge-density-wave (CDW) state of halogen-bridged mixed-valence transition metal complex (MX complex) within mean field theory (MFT), and taken electron correlation into account by second-order perturbation relative to the mean field state. It is seen correlation reduces the dimerization and narrows the band gap further compared with MFT.