  We used classical molecular dynamics and the van Beest Kramer van Santen
(BKS) potential to generate small model systems of amorphous silica. We further
optimized the classically equilibrated configurations using plane wave based
density functional theory and a generalized gradient (GGA) approximation.
Within ab initio treatment we showed that both geometry optimization and
Car-Parrinello annealing lead to the same final configurations but the CPU time
required for the geometry optimization to reach convergence is one fifth of the
time needed by a Car-Parrinello annealing. In addition during the optimization
or the annealing no substantial change occurs on the topology acquired by the
vitreous silica at the end of the classical quenching protocol. Structural and
electronic properties have been calculated and compared to experiments.
