Molecular dynamics simulation of alkali-silicate glass structures

Abstract

The method of molecular dynamics (MD) was used to simulate the structure of R2O–SiO2 (R=Li, Na, K) glasses in an effort to identify compositional fluctuations which could act as precursors to phase separation. Radial distribution functions (RDF) for various ion pairs, vibrational frequencies, and coordination numbers for the various ions, the Si–O–Si and Si–O–R bond angle distributions were calculated. No definite composition fluctuations could be observed with variations in alkali type or content. Significant changes in the basic Si–O network characteristics were, however, observed when the volume was forced to vary. In addition to the usual objections of lack of directionality and unreasonably high fictive temperatures associated with the MD calculations, the problem of defining a molar volume correctly could be equally critical to determine composition fluctuations in the R2O–SiO2 glasses.