Evaluation of structural inhomogeneity by molecular dynamics method. Structural variation of silica glass

Molecular dynamics (MD) simulations for silica glass and melt were carried out to evaluate the inhomogeneity of several structural units. This paper deals with the difference between the time and site variations of bond distances and bond angles, instead of treating MD model glass as a statistically averaged structure. The structural variation of local units, such as SiO bonds and bond angles, showed a characteristic dependence on the temperature; in particular the SiOSi bond angles were distributed from site to site as widely as the time fluctuation at about 3000 K. According to the comparison with the other structural parameters or the thermodynamic properties, they are proved to be a most suitable variable for recognizing the glass transition phenomenon. Using the molecular orbital calculations, the possibility of estimating the inhomogeneity of electronic states is discussed.