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Optical and Raman signatures of polarons in mixed-valent linear chain metal complexes with halogen bridges

The vibrational (Raman) and optical properties associated with the ground state and polaronic defects are compared and contrasted for the charge-density-wave PtX materials belonging to two different regimes: the highly valence localized compound PtCl and the more valence delocalized compound PtBr. The model for PtCl explicitly includes nearest-neighbor Coulomb attraction and metal ion-ion electrostatic repulsion: with increasing valence delocalization this reduces to the linear Peierls-Hubbard model used for PtBr. The results agree well with the available 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 Raman frequencies for electron polarons and bipolarons in PtCl.

vibrational properties; polaronic defects; charge-density-wave; valence localized compound; ion-ion electrostatic repulsion; bipolarons; PtCl; PtCl; Raman frequencies

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