THEORETICAL CALCULATIONS ON SILICA FRAMEWORKS AND THEIR CORRELATION WITH EXPERIMENT

Symmetry-constrained lattice energy minimizations have been performed on a series of pure silica polymorphs using the shell model for silicates. Quantitative agreement is found between the experimental and calculated structures with particularly good agreement being obtained for the fractional coordinates of the atoms in the asymmetric unit. The computed lattice energies of the silicas are found to be between 8 and 20 kJ mol(-1) less than that of quartz. The energies are found to be directly dependent on the densities of the structures and show good agreement with a recent calorimetric study.