  Vitreous silica is the most versatile material for scientific and commercial
applications. Although large-scale atomistic models of vitreous-SiO$_2$
(v-SiO$_2$) having medium-range order (MRO) have been successfully developed by
melt-quench through classical molecular dynamics, the MRO is not well studied
for the smaller-scale models developed by melt-quench using ab-initio molecular
dynamics (AIMD). In this study, we obtain atomistic models of v-SiO$_2$ by
performing melt-quench simulation using AIMD. The final structure is compared
with the experimental data and some recent atomistic models, on the basis of
the structural properties. Since AIMD allows for the estimation of electronic
structure, a detailed study of electronic properties is also done. It shows the
presence of defect states mainly due to dangling bonds in the band-gap region
of electronic density of states, whereas the edge-shared type of defective
structures in the glassy models are found to contribute mainly in the valence
band. In addition, Oxygen and Silicon vacancies as well as bridging Oxygen type
of defects were created and their contributions to the band-gap were studied.
