We clarify the local structure in a model silicon glass by use of Voronoi-polyhedron analysis. The glass is produced by molecular dynamics with a Stillinger-Weber potential. The atoms in the glass are nearly distinguishable:there are about 200 types in the system with 216 atoms. The analysis clarifies that the polyhedra are formed by a small number of large-area polygons or by a large number of smallarea polygons. This feature is different from those in Lennard-Jones glasses or metallic glasses and is attributed to the loose-packed structure even in the glass state, in which the atoms still have directional bonding. The variety of Voronoi signatures that appear in the covalently bonded glass can be simplified mainly into two types of signatures by constructing the polyhedra by use of the bonding atoms.

We analyze for the first time the relation between the shape of the local vibrational densities of states (LDOSs) and the local environments of atoms in glasses. We calculated the LDOSs in model silicon glasses by use of a recursion method. The glasses are produced by a constant pressure molecular dynamics method with a three-body potential by Stillinger and Weber. The transverse optic (TO) peaks reduce in height with an increase of the number of the coordinated atoms. The heights of the TO peaks also decrease with the increase of the number of the coordinated atoms that have (2,3,0) Voronoi signature. The heights of the transverse acoustic peak are insensitive to the number of bonds. The origin of the decrease of the TO peak is discussed. The slopes of the low frequency side of the LDOSs are insensitive to the local structure of the glasses. The long-range force field in the present glass is the same as that in the crystal state.