Determination of the Refractive Parameters in Tl3TaS4

Theoretical calculations of the refractive index, optical dielectric constant and reflection coefficient for the Tl3TaS4 crystal within Harrison(s bonding orbital model were carried out. The detailed analysis of our calculations has been done to present deeper understanding of this investigation. The calculations were performed for the spectral region far from the absorption edge, where the dispersion of the refractive index is absent. The refractive index was determined within the generalized single-oscillator model. This approach allows determining the energies of occupied electronic states using the Hartree-Fock values for the valence levels in solids. We have used the simplification by including only nearest-neighbor couplings (clusters) and using universal parameters, which allows direct prediction of crystal physical properties. This cluster approximation based on a special point is used for calculations of bond polarizabilities. The real part of the dielectric function is determined from the imaginary part by the Kramers-Kronig relationship. Finally, we have used the Moss, Ravindra, Herve and Vandamme models for comparing the value of the refractive index calculated according the Harrison(s model. The satisfactory agreement of our theoretical calculations is obtained. It was shown that Harrison(s model allows analyzing the optical parameters of Tl3XY4 type compounds. The refractive index evaluation is of considerable importance for applications in integrated optic devices, where refractive index of materials is the key parameter for device design. The theoretical technique developed in this paper could be used for the investigation of the optical properties of materials. It should be noted that the crystal under investigation is expected to contribute to the development of nanophysics and personalized medicine for health monitoring and prevention.