Da. Litton et Sh. Garofalini, VITREOUS SILICA BULK AND SURFACE SELF-DIFFUSION ANALYSIS BY MOLECULAR-DYNAMICS, Journal of non-crystalline solids, 217(2-3), 1997, pp. 250-263
Molecular dynamics simulation was used to investigate the kinetics of
self-diffusion in the bulk and on the surface of pristine vitreous sil
ica. Multibody potential functions were used to describe interatomic f
orces, Activation energies were found to be similar for Si and O self-
diffusion and did not vary appreciably between self-diffusion in the b
ulk and an the surface. For both species in the bulk and on the surfac
e, average activation energies ranged from 113-115 kcal/mol. Oxygen se
lf-diffusivity was found to be only slightly higher than silicon self-
diffusivity in the bulk and on the surface. Self-diffusion coefficient
s in the top 3-7 Angstrom of the surface were found to be higher than
those of bulk simulations by less than a factor of two. Self-diffusion
on the surface was observed to occur by motion of SiO3 and SiO4 polyh
edra over several angstroms while bulk self-diffusion involved signifi
cant neighbor exchange over similar length scales, Surface diffusion t
hrough a vapor phase (via desorption and re-adsorption at a distant lo
cation on the surface) was not included in the surface data. (C) 1997
Elsevier Science B.V.