Interaction potential for SiO2: A molecular-dynamics study of structural correlations.

distance. In lattice-structure calculations with the total potential function, a-cristobalite and aquartz are found to have the lowest and almost degenerate energies, in agreement with experiments. The energies for p-cristobalite, p-quartz, and keatite are found to be higher than those for acristobalite and a-quartz. Molecular-dynamics calculations with this potential function correctly describe the short- and intermediate-range order in molten and vitreous states. In the latter, partial pair-distribution functions give Si— 0, 0— 0, and Si— Si bond lengths of 1.62, 2.65, and 3.05 A, respectively. The vitreous state consists of nearly ideal Si(Ol&2)4 tetrahedra in corner-sharing configurations. The Si— U— Si bond-angle distribution has a peak at 142' and a full width at half maximum {FWHM) of 25' in good agreement with nuclear magnetic resonance experiments. The calculated static structure factor is also in agreement with neutron-diffraction experiments. Partial static structure factors reveal that intermediate-range Si-Si, O-O, and Si-0 correlations between 4 and 8 A give rise to the first sharp diffraction peak {FSDP). The FSDP is absent in charge-charge structure factor, which indicates that charge neutrality prevails over length scales between 4 and 8 0 A. Dynamical correlations in vitreous and molten states, phonon densities of states of crystalline and vitreous Si02, infrared spectra of crystalline, vitreous and molten states, isotope effect, distribution of rings and their structure in molten and vitreous states, and structural transformations at high pressures will be discussed in subsequent papers.