O 2p-band

The calculation of the core levels of LajCuO discussed above was performed within the cluster approximation wherein the dependence of the spectral shape on the oxygen band-width is missed out. In order to include the effect of the oxygen 2p derived band on the spectral shape, the core-level photoemission calculation has to be performed within the impurity model which includes the O 2p band-width (instead of a single O 2p level). For reasonable values of the hybridization strength, t, the range of values of A is such that the Cu appears close to the bottom of the... 

Ab initio methods as well as looking at the structure can of course consider band structure. In the first rush of excitement following the discovery of high Tc superconductors, a number of studies on the band structure of cuprates were undertaken. The results of these up to 1989 are reviewed in detail by Pickett. These calculations established that the bands that crossed the Fermi level were antibonding Cu 3d /O 2p bands. Most of them used an LDA functional but these compounds are expected to be strongly correlated and there is experimental evidence for local Coulomb repulsion on Cu(ii) sites. Larbaoui et found that using a GGA functional... 

Fig. 29. Energy loss structure related to the O 2p band in CS7O (a, b) as observed with Hel (surface plasmon) and Hell radiation (volume and surface plasmon). Curve (c) shows the excitation of two surface plasmons in the Hel spectrum with a sample of approximate composition CS7O...

Thermodynamic parameters have been calculated for NbO, and there has been an XPS study of the semiconductor-to-metal transition in Nb02/ During this transition, the Nb 4d band shifts progressively towards the O 2p band with increasing temperature until above the transition temperature the two bands merge. 

The characteristic feature of this band structure is that the properties of the orbitals of the atoms and atomic groups are approximately preserved. The lowest band is primarily an O 2s-band. The next band is primarily an O 2p-band. These bands are fully occupied valence bands. The next band is primarily of t2 character the following band primarily of Og character. These bands are unoccupied and are called conduction bands. The Fermi level in the ideal crystal is between the highest occupied and the lowest unoccupied bands. The band gap of 3,2 eV makes Ti02 an insulator. 

The band structure computed in Rgure 8 has 12 O 2p bands, 6 g bemds, 4 bands simpiy because the unit ceil contains two formula units, (TiC )2. There is ntn one reciprocal space varieible, but several lines (T X, X M, etc.) that refer to directions in the three-dimensional Brillouin zone. If we glance at the DOS, we see that it does resemble the expectations of 21. There are well-separated 0 2s, 0 2p, Ti g and eg bands. 

Fig. 10. A combination of the XPS and BIS spectrum of CeOj (Allen 1985a), similar data have been pubhshed by Wuilloud et al. (1984). The Fermi energy is in the gap between the O 2p band and the Ce 4f state, showing that CeOj is an insulator. There is, however, strong mixing between the 02p and Ce4f wave-functions (Koelling et aL 1983X...

Figure 16 Intensities of the total O 2p band emission for the TiC(lll)-(l X 1)0 and TiC(lOO)-(1 X 1)0 systems as a function of photon energy.

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