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This paper presents a systematic first-principles study of phonons and Raman spectra of cubic Hg 3 Te 2 Cl 2 within a framework of DFT in the GGA/PBE approximation. The phonon dispersion, total and partial density of vibrational states for Hg 3 Te 2 Cl 2 crystals are analyzed. The identification of the vibrational modes at the Brillouin zone center is conducted and discussed in details. The first-principles calculated Raman-active phonon frequencies and simulated Raman spectra are compared with experimental data. The assignment of the phonon lines to define atomic vibrations was made on the basis of their symmetries in close comparison with results of lattice-dynamical calculations. Satisfactory agreement is obtained with experimental mode frequencies.

The interrelation between structural and optical properties of the Hg 3 S 2 Cl 2 polymorphs have been theoretically investigated. This paper presents the results of calculations of the refractive indices and reflection coefficients for (α), (β), (γ) – Hg 3 S 2 Cl 2 crystalline phases using the Harrison bonding-orbital method. The refractive indices in the spectral region far from the absorption edge were determined within the generalized single-oscillator model. The Hartree-Fock values for the valence levels were used for evaluation the energies of filled electronic states in Hg 3 S 2 Cl 2 crystals. By analyzing the polarizability and susceptibility χ it is possible to calculate the refractive index and reflection coefficient; moreover the performed calculations demonstrate a satisfactory agreement with experimental results.