Embedded microclusters in zeolites and cluster beam sputtering -- simulation on parallel computers. Progress report, September 1993--September 1994

摘要

We have designed a time-space multiresolution approach for large-scale molecular-dynamics (MD) simulations involving long-range Coulomb forces and three-body interactions. This approach has been implemented on various parallel architectures including the 512-node Intel Touchstone Delta at Caltech and the 128-processor IBM SP1 at Argonne National Laboratory. Parallel MD simulations involving 1.12-million particles have been performed to investigate the pore interface growth and the roughness of fracture surfaces in porous silica. When the mass density is reduced to a critical value, pores grow catastrophically to cause fracture. The roughness exponent for internally fractured surfaces, (alpha) = 0.87 (+-) 0.02, supports experimental claims about the universality of (alpha). A reliable interatomic potential has been developed for MD simulations Of Si(sub 3)N(sub 4). The nature of phonon densities-of-states due to low-energy floppy modes in crystalline and glassy states has been investigated. Floppy modes appear continuously in the glass as the connectivity of the system is reduced. In the crystal, they appear suddenly at 30% volume expansion. The density-of-states due to floppy modes varies linearly with energy, and the specific heat is significantly enhanced by these modes. Thermal conductivities of ceramic materials are calculated with a nonequilibrium MD method and the Kubo-Greenwood formula using a parallel eigensolver and the parallel MD approach. The calculations for amorphous silica agree well with experiments over a very wide range of temperatures above the plateau region. Currently, we are investigating thermal transport mechanisms in technologically important materials - porous glasses, nanophase ceramics, and zeolites.