  We present the results of large scale computer simulations in which we
investigate the structural and dynamic properties of silicate melts with the
compositions (Na_2O)2(SiO_2) and (Al_2O_3)2(SiO_2). In order to treat such
systems on a time scale of several nanoseconds and for system sizes of several
thousand atoms it is necessary to use parallel supercomputers like the CRAY
T3E. We show that the silicates under consideration exhibit additional
intermediate range order as compared to silica (SiO_2) where the characteristic
intermediate length scales stem from the tetrahedral network structure. For the
sodium silicate system it is demonstrated that the latter structural features
are intimately connected with a surprising dynamics in which the one--particle
motion of the sodium ions appears on a much smaller time scale than the
correlations between different sodium ions.
