IONIC INTERACTION IN A PLATINUM CHLORIDE LINEAR-CHAIN - PTCL

We have modified our previous model of MX chain materials to better de scribe the highly valence localized platinum chloride linear chain com pounds, e.g., PtCl. The nearest neighbor Coulomb attraction and metal ion-ion electrostatic repulsion are added to our previous Hamiltonian. These two interactions play two roles: generating (i) an effective an harmonic intra-site electron-phonon coupling (therefore leading to the formation of charge-density-wave even if the inter-site electron-phon on coupling is weak) and (ii) acting as an effective elastic force bet ween neighboring Pt and Cl atoms. Uniform and various defect states (p olaron, bi-polaron and exciton) have been studied within this framewor k by computing their optical absorption, resonance Raman (RR) and infr ared spectra. The results agree with the experimental data very well. Buckling of Cl atoms out of the chain is found to be important in orde r to obtain correct frequencies of RR modes of electron polarons and b i-polarons.