Molecular dynamics calculations for Mg₃Al₂Si₃O₁₂ (pyrope) and Ca₃Al₂Si₃O₁₂ (grossular) glass structures

The structures of pyrope (Mg₃Al₂Si₃O₁₂) and grossular (Ca₃Al₂Si₃O₁₂) glasses at 300 K have been analyzed by molecular dynamics (MD) simulation techniques. The calculated glass structures have been compared with the structures obtained by the X-ray diffraction method. The averaged structures are in good agreement with the results of X-ray analyses, indicating that these MD-derived structures represent well the real glass structures. The calculated pair correlation functions of SiO and AlO pairs for pyrope glass show broader peaks than those of grossular glass, which may indicate that Mg²⁺ ions give a larger effect on the network structure of SiO₄ and AlO₄ tetrahedra. The calculated structures include AlOAl arrangements, which indicate that these structures do not well obey the aluminum avoidance principle. Numbers of AlO₄ tetrahedra in these glasses show the presence of Q₄ species greater than SiO₄ tetrahedra. In these glasses, the O (Si + Al) ratios are 2.4. Therefore, it is expected that some Al³⁺ ions work as network modifier ions in these glasses.