Silica under very large positive and negative pressures: Molecular dynamics simulations on parallel computers

A highly efficient multiresolution algorithm has been developed to carry out large-scale molecular dynamics (MD) simulations for systems with long-range Coulomb and three-body covalent interactions. The algorithm combines the reduced cell and fast multipole methods and multiple time-step approach. Pressure-induced structural transformation, loss of intermediate range order, and dynamical correlations in SiO2 glass are investigated with the molecular-dynamics method. At twice the normal density, the Si - O bond length increases, the Si - O coordination changes from 4 to 6, and the O - Si - O band-angle changes from 109 to 90°. This is a tetrahedral-to-octahedral transformation, which was reported by Meade, Hemley, and Mao. Results for phonon density of states also reveal significant changes at high pressures. The multiresolution M D approach has been used to investigate the structural properties and mechanical failure in microporous silica. Structural correlations are characterized by the fractal dimension, internal surface area, and pore surface-to-volume ratio. Critical behavior at fracture is analyzed in terms of pore percolation, and kinetic roughening of fractured surface is also investigated. © 1996 Plenum Publishing Corporation.