Electronic band model

As will be shown in the following sections the results of the one-electron band structure calculations allow to describe several important properties of the tetracyanoplatinates, like the dominance of the Pt 5 dz2 and Pt 6 p2 orbitals for the red-shift of the main optical transitions with decreasing metal-metal distance82 6, the admixture of Pt(6pz, CNji ) character into the valence band82,89, or several stabilization effects upon partial oxidation84. On the other hand, a series of experimentally found features is out of the scope of the one-electron band model. In the following some of these properties are specified ... 

Two complementary models can be developed to describe the features mentioned above. Both models consider the electron-electron interaction and the exciton-lattice interaction. Although both models have different starting points, they yield satisfying interpretations of the experimental findings. The one model is the model of Wannier excitons which ensues directly from the one-electron band model discussed above. The other one starts from the many electron states of the [Pt(CN)4]2 ion and takes into account the coupling between neighbouring complex ions. 

Fig. 4. 22. Qualitative one-electron band model for the bonding in TiO, (modified figure after Goodenough, 1971).

Fig. 6.1. The electronic structure of ZnS (a) simplistic qualitative one-electron MO energy-level diagram for a ZnS4 (tetrahedral) cluster (b) simplistic one-electron band model for ZnS.

Even though we have made considerable effort to explore the reciprocal lattice because it allows us to determine the actual location of the bonding electrons in any given three-dimensional lattice, it should be clear that the electron-band model is easier to understand and easier to use than the Reciprocal lattice band model. To date in this discussion, we have covered ... 

THE PHYSICAL BACKGROUND One-dimensional electronic band model... 

With these reservations in mind we proceed with Eq. (5.1) and the one electron band models in describing the electrical properties. Major difficulties in applying these models to the experimental data wiU hopefully guide us to identify the weaknesses of this simplified approach. A brief discussion of the effects of heterogeneity is deferred to Section 5.4. 

A similar approach will be used here [37], but one based on more recent electron band models. 

The one-electron band model which has been used so successfully to interpret the photoelectron spectra of the valence bands of many metals clearly will not be satisfactory by itself to interpret the 4f spectra of Ce. Indeed, self-consistent band calculations for both y- and a-Ce yield a 4f band about 1 eV wide which straddles the Fermi level (Glotzel 1978, Pickett et aL 1981, Podloucky and Glotzel, 1983). The filled portion extends only 0.1eV below the Fermi level and contains approximately one electron. It is hybridized with other states and is not a pure 4f band. The simple one-electron picture of photoemission based on these bands would predict a narrow 4f-derived peak at the Fermi level in both phases of Ce, and this is not observed. To describe adequately the photoemission spectra, we must then move beyond the one-electron picture. As discussed above, photoelectron spectra dxt final state spectra which reflect the initial states to a greater or lesser extent depending on the localization of the states themselves. 

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