Abstract
Ab initio molecular orbital calculations have been carried out for silicate, aluminosilicate, and aluminate clusters in order to study the NMR characteristics of oxygen sites that are possibly present in the structure of aluminosilicate glasses and melts. Of particular interest are the different types of bridging oxygens (oxygens bonded to two tetrahedrally coordinated Si and/or Al) and tricluster oxygens (oxygens linked to three tetrahedrally coordinated Si and/or Al). The calculated values for the 17O quadrupolar coupling constants (QCC) of Si−O−Si, Si−O−Al, and Al−O−Al bridging oxygens agree reasonably well with experimental NMR data for similar oxygen sites in crystalline silicates, aluminosilicates, or aluminates, and do not show significant dependence on the basis set and theory (Hartree−Fock vs density functional theory) of calculations. The calculated values for the 17O isotropic chemical shift (δiO), on the other hand, show large dependence on the basis set and method of calculations, although th...
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