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Long-Range Coulomb Interaction in the Halogen Bridged Mixed Valence Transition Metal Compound PtCl

We investigate the role played by the long-range Coulomb interaction (Madelung field) in the linear chain compound of halogen bridged mixed valence transition metal, PtCl. The long-range Coulumb interaction is very important when we deal with the defect states (e.g. polaron, exciton) in a highly localized CDW material like PtCl. We simulate the system numerically by adding the long-range Coulomb field V term to an extended two band 3/4 filled Hubbard model, which also includes the electron phonon interaction. V has the effect of changing the force constant and the electron phonon coupling. We find that there is arbitrariness in choosing V to agree with the experimental results for the undoped ground state properties. In the defect states, however, the V term plays a crucial role because the defect states, having locally changed charge distributions, are very sensitive, for local electronic and phonon modes, to the local Coulomb term.

Halogen Bridged Mixed Valence Transition Metal Compound

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