Abstract
A model for the description of charge orderings and distortions in complex TCNQ salts involving intra- and interchain electron interactions and electron-lattice couplings is investigated. Its thermodynamical properties are analysed in the limit of infinitely strong intramolecular Coulomb repulsion, treating intermolecular interactions within the two-sublattice H-F approximation. Stability conditions for various types of orderings are determined. Site charge ordering and dimerization accompanied by bond charge ordering are found to coexist only in a limited range of parameters diminished by the hopping and the electron-phonon coupling via Coulomb forces. Depending on the value of the latter, interaction phase transitions in the system can be continuous or not. Intermolecular Coulomb interaction stabilizes site charge ordering but it can also essentially enhance transition temperatures and energy gap in dimerized phases. For experimentally reliable values of parameters the energy gaps predicted by the model are in good agreement with those observed in D +(TCNQ) − 2.
Published Version
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