Abstract
As discussed in Chapt. 2, weakly overlapping π-molecular orbitals provide a useful starting point for estimating the electronic states for molecular ma- terials. As an input for such tight-binding band-structure calculations, the molecular orbitals are usually calculated within the extended-Hückel approxi- mation which uses some empirical molecular parameters [169, 170, 82, 79, 81]. As has been discussed in more detail in [86], the extended-Hückel approxima- tion enables the calculation of the overlap integrals S and the corresponding transfer energies t between the π-orbitals of adjacent molecules. The latter quantity is a measure of the probability for an electron to hop from one molecule to the next. The so-derived extended-Hückel tight-binding bands have the usual cosine energy-dispersion relation
where a, b, and c denote the intermolecular distances along the a-, b- and c- axes, k =(k a , k b , k c ) the wave vector of the electron and t a , t b and t c the directional-dependent transfer energies. For simplicity, a lattice with or- thorhombic symmetry has been assumed. This semi-empirical method has been very successfully applied in the case of the present molecular metals, see, e.g. [80, 82, 171, 96, 109, 172, 173, 174]
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© 2007 Springer-Verlag Berlin Heidelberg
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(2007). Normal-State Properties. In: Low-Dimensional Molecular Metals. Springer Series in Solid-State Sciences, vol 154. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-540-49576-5_4
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DOI: https://doi.org/10.1007/978-3-540-49576-5_4
Publisher Name: Springer, Berlin, Heidelberg
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