The dielectric function e which connects the dielectric displacement and the electric field vector is closely related to the susceptibility χ :

 .

The frequency dependence of the susceptibility is very characteristic for a material since it incorporates vibrations of the electronic system and the atomic cores as well as contributions from free charge carriers.

The following susceptibility types are supported by SCOUT:

•Constant

•Constant refractive index

•Harmonic oscillator

•Drude model for free carriers

•Extended Drude model

•Brendel oscillator

•Kim oscillator

•Gervais oscillator

•User-defined formula

•Imported data

•KKR susceptibility

•KKR susceptibility II

Appropriate models for interband transitions are discussed in the section on KKR dielectric function models.