TOPOLOGICAL EFFECTS ON THE BAND STRUCTURE OF SILICA.

Under some circumstances, the electronic and the vibrational properties of silica networks can be expressed in terms of the Connectivity Matrix. This matrix contains information about the connectivity of the network, and its properties are fairly well understood as a result of extensive studies on silicon networks. If the range of the overlap parameters becomes too large, this description breaks down and structural parameters such as the dihedral angle enter in an unavoidable way. In crystalline forms of silica, traditional band structure methods are far superior to this approach. However in comparing crystalline and vitreous silica, it is useful to have a common language when discussing the main features in the density of states. A detailed discussion is given for the oxygen 2s band in silica.