Valence-bond analysis of extended Hubbard models: Charge-transfer excitations of molecular conductors

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Abstract

The low-energy charge transfer (CT) excitation characteristic of both -molecular conductors and complex-ion-radical salts is interpreted as a nearest-neighbor Coulomb interaction V that is comparable to the bandwidth, 4|t|. Partly filled segregated regular stacks in organic conductors are represented by extended Hubbard models, whose exact CT energies and intensities are obtained by diagrammatic valence-bond (VB) methods for four electrons on finite rings and chains, together with an approximate treatment of V in partly filled infinite stacks for infinite on-site correlations U. Finite V4|t| yields an intense low-lying CT band, containing V and U-2V excitations, that depends weakly on the band filling. Finite V also splits the usual CT absorption around U for half filled bands into strong absorptions around U-V, weak ones around U, and much weaker bands around U+V and U+2V. The CT spectra of mixed-valence tetrathiofulvalene (TTF) salts are modeled with V0.4 eV, U1.4 eV, and |t|0.10-0.13 eV. Similar CT transitions in complex tetracyanoquinodimethane (TCNQ) salts are consistent with the insensitivity of the V peak's position to the filling or the structure. Restricting the basis to one valence state per site produces several general consequences for dipole-allowed optical transitions.

Original languageEnglish (US)
Pages (from-to)2810-2823
Number of pages14
JournalPhysical Review B
Volume23
Issue number6
DOIs
StatePublished - 1981
Externally publishedYes

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Hubbard model
Charge transfer
conductors
charge transfer
valence
excitation
Salts
salts
Organic conductors
Optical transitions
Coulomb interactions
optical transition
Ions
dipoles
bandwidth
Bandwidth
energy
Electrons
sensitivity
rings

ASJC Scopus subject areas

  • Condensed Matter Physics

Cite this

Valence-bond analysis of extended Hubbard models : Charge-transfer excitations of molecular conductors. / Mazumdar, Sumitendra; Soos, Z. G.

In: Physical Review B, Vol. 23, No. 6, 1981, p. 2810-2823.

Research output: Contribution to journalArticle

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