Calculation and analysis of vibrational spectra of PbCl2-Sb2O3-TeO2 glass from first principles

Ternary PbCl₂-Sb₂O₃-TeO₂ system provides promising materials for photonic applications. Glasses in this system are thermally stable, their refraction index is about 2.2 and they are transparent from 400 nm up to 6 μm. The ab initio molecular dynamics (MD) simulations of xPbCl₂-10SbO_3/2−(90-x)TeO₂ glasses (x = 10, 20, 30, 40, and 50) were carried out using density functionals, the plane-wave basis set expansion, and the projector-augment waves (PAW). The resulting glassy structures were analyzed with the help of partial radial distribution functions (RDF) and partial coordination numbers. Good agreement with the available experimental data was confirmed. The axial and equatorial oxygen atoms of TeO₄ trigonal bi-pyramids were distinguished. Vibrational frequencies and their corresponding eigen-modes were found by diagonalization of the dynamical matrix. The simulated vibrational spectra were decomposed to determine the contributions from individual atomic species and some more complex structural features and compared with experimental Raman spectra. The spectral decomposition was carried out by projecting vibrational displacement vectors onto various normal modes of typical symmetric structural units. The method proved to be able to successfully interpret the experimental Raman spectra.