INTERATOMIC POTENTIALS AND THE STRUCTURAL-PROPERTIES OF SILICON DIOXIDE UNDER PRESSURE

First-principles interatomic potentials based on ab initio Hartree-Fock self-consistent-field calculations have recently been proposed for silicon dioxide. These pairwise potentials yield accurate ambient-pressure internal-structure parameters and dynamically stable polymorphs for several known forms of silica. We use these potentials to analyze crystallographic data for quartz under pressure. We find the potentials do not describe the changes in the internal parameters of quartz under pressure. Specifically, the potentials do not give the correct trends for the O-Si-O angles or the c/a lattice-constant ratio. We have included bond-bending terms to modify the pairwise potentials. If the angles in question are fit to reproduce the experimental data, then the bulk modulus is in poor agreement with experiment. Our findings reinforce the need for a covalent term in the interatomic potential, which is not based on quadratic expansions of bond-bending and -stretching forces. © 1990 The American Physical Society.