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 silica tes. Quantitative agreement is found between the experimental and calc ulated structures with particularly good agreement being obtained for the fractional coordinates of the atoms in the asymmetric unit. The co mputed lattice energies of the silicas are found to be between 8 and 2 0 kJ mol(-1) less than that of quartz. The energies are found to be di rectly dependent on the densities of the structures and show good agre ement with a recent calorimetric study.