OPTICAL AND RAMAN SIGNATURES OF POLARONS IN MIXED-VALENT LINEAR-CHAINMETAL-COMPLEXES WITH HALOGEN BRIDGES

The vibrational (Raman) and optical properties associated with the gro und state and polaronic defects are compared and contrasted for the ch arge-density-wave PtX materials belonging to two different regimes: th e highly valence localized compound PtCl and the more valence delocali zed compound PtBr. The model for PtCl explicitly includes nearest-neig hbor Coulomb attraction and metal ion-ion electrostatic repulsion: wit h increasing valence delocalization this reduces to the linear Peierls -Hubbard model used for PtBr. The results agree well with the availabl e experimental data for PtCl and PtBr. Buckling of Cl atoms out of the chain axis is found to be important in order to obtain the observed R aman frequencies for electron polarons and bipolarons in PtCl.