Structural properties of molten silicates from ab initio molecular-dynamics simulations: comparison between CaO-Al${}_2$O${}_3$-SiO${}_2$ and SiO${}_2$

Abstract

We present the results of first-principles molecular-dynamics simulations of molten silicates, based on the density functional formalism. In particular, the structural properties of a calcium aluminosilicate $[$ CaO-Al${}_2$O${}_3$-SiO${}_2$ $]$ melt are compared to those of a silica melt. The local structures of the two melts are in good agreement with the experimental understanding of these systems. In the calcium aluminosilicate melt, the number of non-bridging oxygens found is in excess of the number obtained from a simple stoichiometric prediction. In addition, the aluminum avoidance principle, which states that links between AlO${}_4$ tetrahedra are absent or rare, is found to be violated. Defects such as 2-fold rings and 5-fold coordinated silicon atoms are found in comparable proportions in both liquids. However, in the calcium aluminosilicate melt, a larger proportion of oxygen atoms are 3-fold coordinated. In addition, 5-fold coordinated aluminum atoms are observed. Finally evidence of creation and anihilation of non-bridging oxygens is observed, with these oxygens being mostly connected to Si tetrahedra.

20 pages, 9 figures, 1 table. Physical Review B, in press

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