| Dispersion models in newAD2 are represented by complex dielectric tensor, generally dependent on the light frequency (or equivalently wavelength, wavenumber or energy), temperature and other implemented variables. Most of the dispersion models are, however, implemented simply as dielectric function dependent only on the light frequency. The dielectric function is then multiplied by unit tensor, representing isotropic environment.
Dispersion models implemented in newAD2 can be separated into five categories:
- Empirical dispersion models
As exception, these models don't have to fulfill basic conditions for dispersion models, such as Kramers-Kronig relations, time-reversal symmetry and sum rule (or at least integrability). The main reason for implementation of these models is compatibility. Generally, use of the empirical dispersion models is not recommended, even though in they can give sufficient results in some special cases or limited spectral region. Same correct result can be acquired by modern models which are, however, more complicated to describe mathematically.
- Elementary dispersion models
These models represent elementary excitations in matter from which user can compose arbitrary dielectric response or extend existing model with these excitations. The models are meant mainly for development of advanced dispersion models.
- Special dispersion models
These models are not dispersion models in strict sense, but represent tool how to create more complicated models in newAD2 from other dispersion models.
- Advanced dispersion models
These models are constructed for description of very well defined materials. Models implement apart from dispersion dependency a lso dependencies on the temperature, pressure etc. Moreover, from user standpoint the models depend only on limited number of material parameters.
- Universal dispersion model
Universal dispersion model (UDM) is most commonly used model able to describe arbitrary dielectric response of condensed matter and it is also suitable for standard description of specific materials. Note that in newAD2 the possibility to describe material with tabulated values is not implemented. All materials have to be modeled by suitable dispersion models. Originally, the model was constructed to describe dielectric response of disordered condensed matter in wide spectral range. As was shown, it is also able to describe optical constants of crystalline materials with sufficient precision. Therefore UDM is suitable for standard description of all condensed matter, which justifies usage the "Universal" word in its name.
modelfile
Dispersion models are listed in media section:
media: id = modelname[:attributes] ...
Example
media: a = Vacuum f = Universal s = c-Si:C:OThis defines three media. Medium
a is defined as dispersion model Vacuum which is trivial dispersion model represented by unit tensor. Second medium f (film) is defined with universal dispersion model and third medium s is defined with advanced dispersion model of high resistance intrinsic crystalline silicon with carbon and oxygen admixtures (Czochralski silicon). Note that arbitrary string can be used as media identifier.
Foregoing definition generate the following parameters:
newAD2> par Nvcf = 500 fixed (0,inf) eV2 Egf = 6 fixed (0,15) eV Ehf = 20 fixed (Egf,70) eV fOs = 0 fixed [0,1000) ppm fOps = 0 fixed [0,100] % fCs = 0 fixed [0,1000) ppm newAD2>
