Model dielectric function

Bergman effective medium theory, in conjunction with a model dielectric function for the particles, has been used. For the other layers the Bruggeman effective medium theory was used. After [Bel6]. 

In the IR spectral region, DFs i(ui) are sensitive to phonon and plasmon contributions. Hence, IR model dielectric functions (MDFs) are written as the sum of lattice and free-charge-carrier fcc(u ) contributions [73]... 

Visible-to-Vacuum-Ultraviolet Model Dielectric Function Band-to-Band Transitions and their Critical-Point Structures... 

Although many improvements have been proposed for the calculation of the dielectric response function from first principles [31,32], still this stage is both computer time and memory very demanding when a large basis set is used for the description of the electronic structure. Efficient GW methods have thus been developed, in which a model dielectric function is used to mimick the screening properties of the system under study [28,33,34]. 

The term 3(— l/e q, co)) is referred to as the dielectric loss function. Structures in this function can be correlated to bulk plasmon excitations. In the vicinity of a surface the differential cross section for inelastic scattering has to be modified to describe the excitation of surface plasmons. The surface energy loss function is proportional to 3(—l/e(, cu) + 1). In general, the dielectric function is not known with respect to energy and momentum transfer. Theoretical approaches to determine the cross section therefore have to rely on model dielectric functions. Experimentally, cross sections are determined by either optical absorption experiments or analysis of reflection energy loss spectra [107,108] (see Section 4.3). 

Fig. tr.1-157 ZnS, cubic. Dielectric-function spectrum e E), measured by spectroscopic ellipsometry at 300 K after chemomechanical polishing of the sample (circles). The solid lines show values calculated from a model dielectric function for interband critical points. The dashed lines represent the best-fit standard critical-point lineshapes [1.132]... 

In this form it is evident that the first term on the right-hand side gives the screened exchange. The second term is obviously the potential from the "Coulomb-hole" in the charge density around a given electron. The COHSEX approximation has been used for Si in gn gction with various Penn-type model dielectric functions... 

Figure 1.10 Fitted result of the model dielectric function of Equation (1.38) to the experimental e(E) data of Cu listed in this book.

In the infrared spectral region, the dielectric function ej(o)) is sensitive to phonon and plasmon contribution. Therefore, the infrared model dielectric function can be written as a sum of lattice, sj (co) and free-charge carrier. 

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