In the recent years, the Virtual Coater approach was developed for a complete theoretical modeling of physical deposition processes. The concept is based on the combination of different simulation techniques to a powerful multiple scale model. Thereby, the single simulation methods are chosen well with respect to the physical topic. In the simulation, the material transport and the processes in the coating plant are simulated by DSMC (Direct Simulation Monte Carlo). Achieving a high practical relevance, the simulations are performed on the basis of real existing magnetron and ion beam sputtering coaters. The DSMC simulation delivers the physical behavior of the atoms at the substrate, which can be used for the atomistic simulation. Using classical molecular dynamic simulations the virtual material is deposited, which delivers the structural properties dependent on the growth conditions on the substrate. Actually, the structures differ and consequently, a change in the optical and electronic properties is observed. The refractive index of a solid can be determined by ab-initio calculations. Generally, the density functional theory delivers the dielectric function applying Kramers Kronig relation. Thereby, the mass density, the stoichiometry and the material is included in the computation. With respect to the structural size of only few hundred atoms, the structural properties cannot be respected. Alternatively, the effective medium theory considers the structural properties of the thin film. Both, the effect of the amount and size of voids as well as the pores orientation are implemented in the calculation of the effective index of refraction. However, the effective medium theory requires the knowledge of the refractive index of the structure material as well as of the pores material. Both models allow to describe the material behavior in a specific range. The DFT is addressed to dense and homogeneous materials and the effective medium theory implements the structural properties. The combination of the theoretical approaches leads to a more general description of the refractive indices. The resulting behaviors are compared and the validness of the model is discussed and linked to experimental results of manufactured coatings.