We performed charge analysis and vibrational calculations using a cluster model (see Fig- Hirshfeld charge calculation was carried out at the DFT B3LYP/6-31+G** level of theory using the Gaussian16 program. Normal mode analysis was performed at the levels of B3LYP/6-31+G** and PBE+D3/6-311+G**. Only the AlO 4 tetrahedra and the adjacent SiO 4 tetrahedra were relaxed (see Figure ).