Neighborstrand Interactions in One-Dimensional Tight-Binding Models. The (Tetrathiosquarato)nickel(II) System
In this chapter we analyze band structure properties of quasi 1D systems under the influence of interchain interactions. The necessary coupling elements are approximated by the electrostatic self-consistent-field (SCEF) formalism derived in section III.4. Two aspects will be discussed in some detail: i) variations of the dispersion curves, charge distributions, etc. as a function of structural building principles realized in the solid and ii) possible formations of symmetry broken solutions of the charge density wave (CDW) or bond-order alternation wave (BOAW) type as response to magnifications of the “field strength” experienced by the 1D reference chain. Experimental investigations have shown that interactions which are higher than 1D (i.e. interchain coupling) or CDW/ BOAW solutions in the donor and acceptor units of a segregated DA stack are often desirable to observe high electric conductivities [IV.1–IV.3]. Recent numerical studies on the significance of higher dimensionalities in donor-acceptor systems are either based on one-electron calculations of the Wolfsberg-Helmholtz (WH) type [IV.4, IV.5] or on physically transparent phenomenological model Hamiltonians which can be treated analytically [IV.6]. It lies in the nature of simple one-electron Hamiltonians that it is not possible to detect any symmetry broken solutions.
KeywordsValence Bond Charge Density Wave Interchain Interaction Acceptor Unit Symmetry Break
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