Halogen-bridged mixed-valence complexes as paradigms of strongly interacting low-dimensional systems: Ground state

Abstract

The microscopic parameters of a representative halogen-bridged transition metal complex -[Pt(en) 2][Pt(en) 2Cl 2](ClO 4) 4- are extracted from the literature optical data on the basis of a simple phenomenological model. Proper account of electron-molecolar vibration coupling allows one to reproduce satisfactorily the experimental data, clarifying the relevance of this interaction in respect of the electron-electron ones. The ground state of mixed-valence complexes is rationalized through Valence Bond calculations which solve exactly the extended Hubbard model for finite clusters with alternating on-site energies. The calculations allow a sound comparison with other half-filled systems like polyacetylene (CH) x or charge-transfer salts.