Cluster-based DFT modeling of Raman vibrations in tetrahedral GeS

The local atomic structure of amorphous chalcogenides remains a decisive factor governing their physical behavior. However, in thin films, structural complexity and high defect concentrations make interpretation of experimental data—particularly Raman spectra—difficult. In this work, we employ cluster-based density functional theory (DFT) modeling to elucidate the structure-vibration relationship in amorphous GeS2 and GeSe2 systems. Using the PBE0 hybrid functional with def2-TZVPP basis and dispersion corrections, we calculated Raman-active vibrational modes for structural clusters representing corner- and edge-sharing tetrahedra, homopolar bonds, and chain fragments. The simulated spectra were compared with experimental Raman data for bulk glasses and sputtered thin films. The calculated modes reproduce the main experimental features and allow direct assignment of the characteristic peaks to specific structural motifs, including Ge–Ge and Ch–Ch (Ch = S, Se) bonds. Extension of the model toward larger six-tetrahedra clusters demonstrates that the method remains consistent with experiment and can approximate medium-range order. The results validate cluster-based DFT as a reliable framework for linking local structure to vibrational response in amorphous Ge–S and Ge–Se systems and provide a foundation for studying defect-related states and impurity effects in chalcogenide thin films.