Results of band structure calculations

Experimental values of Fe moments in Y2Fe14B as obtained by means of polarized neutron studies (Givord et al. 1985d) and 57Fe Mossbauer effect measurements (R. Fruchart et al. 1987) are given in the first and second line of table 13. In the bottom part of the table results of three different types of band structure calculations are given. 

Comparision of the Fe moments at the six Fe sites in R2Fe14B obtained by polarized neutron studies and 57Fe Mossbauer spectroscopy with those derived from band structure calculations. All values are given in Bohr magnetons per Fe atom. 

This spin density distribution is consistent with the observation that the spin moment of the R atoms and transition metal moments couple antiferromagnetically in R2Fe14B. The same type of moment coupling was also found in simpler band structure calculations reported by Szpunar and Szpunar (1985) for Nd2Fe14B. The Fe moments found by the latter authors are given in the next-to-last line in table 13. 

An attempt to describe the magnetocrystalline anisotropy in Y2Fe14B by means of band structure calculations was made by Itoh et al. (1987). These authors derived values for Ku K2 and K3 in Y2Fe14B by calculating the electronic energy for four different spin directions ([001], [100], [101] and [110]). The results are not very convincing since the value calculated for Kx is negative ( — 3.73 MJ/m3) whereas the experimental values is positive (0.80 MJ/m3 see table 5). 

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In solid state physics, the sensitivity of the EELS spectrum to the density of unoccupied states, reflected in the near-edge fine structure, makes it possible to study bonding, local coordination and local electronic properties of materials. One recent trend in ATEM is to compare ELNES data quantitatively with the results of band structure calculations. Furthermore, the ELNES data can directly be compared to X-ray absorption near edge structures (XANES) or to data obtained with other spectroscopic techniques. However, TEM offers by far the highest spatial resolution in the study of the densities of states (DOS). 

All four superconducting systems are metallic above their transition temperature, which agrees with the results of band structure calculations.31 34 What is, perhaps, puzzling, yet extremely useful in attempting to assess possible mechanisms for superconductivity is the observation that other compounds with similar structural features are not superconductors. In addition to LnNiBC (BC3- dimers), these include CaC2 (Cf dimers),... 

Fig. 4.23. Results of band-structure calculations on TiO, using the SCF aug-mented-spherical-wave method. Shown are the total densities of states and the site-projected partial densities of states for Ti 3d, O 2s. and O 2p (normalized to one atom) (after Schwarz, 1987 reproduced with the publisher s permission).

The interpretation of photoemission spectra of the valence band is straightforward in the itinerant limit. In this case the band states are spread across the N unit cells of the crystal and the change in electronic density in a single unit cell is proportional to 1 /N and should be negligible. Then the band energies represent well the excitation spectrum if the appropriate scattering cross-sections are taken into account. This is the case of compounds with a broad 5f band, where the photoemission spectra correlate well with the results of band-structure calculations (Naegele et al. 1988). 

The above information concentrates mainly on UX3 compounds while the experimental data on the analogs with Th or heavier actinides are very scanty. A number of spectroscopic and Fermi-surface studies available for UX3 compounds together with results of band-structure calculations and the systematic behaviour observed across the series of light actinides offer the possibility to draw more general conclusions for this system of AnX3 compounds. 

Results of band structure calculations made for the minority spin direction around T for several other compounds have been included in fig. 39. An assessment of the strengths of the magneto-optical transition in the various materials can be... 

We have re-analyzed the available data in comparison with the results of band structure calculation to provide the basis for an understanding of the electronic structure of the four principal forms of poly aniline the fuUy reduced leucoemeraldine, (1 A)n the partially oxidized emeraldine base, [(1 A)(2A)]n the oxidized and fully protonat emeraldine salt, [IS] (A )n and the fully oxidized bipolaron lattice, (-B-NH+=Q=NH+-)n. 

The photoemission studies so far reported in the literature comprise crystalline and amorphous alloys of early (Tg) and late (Tl) transition metals with either Zr (Amamou, 1980 Oelhafen et al., 1979, 1980) or Gd (Giintherodt and Shevchik, 1975 Shen et al., 1981). These studies have contributed significantly to the understanding of the electronic structure of amorphous as well as crystalline alloys, especially now that the results of band structure calculations have become available for most of the materials investigated (Kiibler et al., 1981 Oelhafen et al. (1982), Moruzzi et al., 1983). 

Mj(Oy Mill) X-ray emission from electron excited elemental Eu and Gd was registered by Mariot et al. (1974). The M emission intensity from Gd was found to be five times larger than that from Eu. This finding is in qualitative agreement with the result of band-structure calculations (Freeman 1971, McGuire 1972), which confirm that the density of occupied 5d states should be large in Gd and small in Eu. 

The crystal structure determination of y-(EDT-TTF)[Pd(dmit)2] by an IP system was performed at 18 K. The results of band structure calculations are shown in Figure 5.40. 

Various forms of the exchange-correlation potential have been proposed in the literature (29-35). Fortunately, the results of band structure calculations frequently do not depend much on the choice of the exchange-correlation potential. However, differences up to about 25 mRyd can occur when different exchange-correlation potentials are applied. 

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