  A combination of molecular-dynamics (MD) computer simulation and
mode-coupling theory (MCT) is used to elucidate the structure-dynamics relation
in sodium-silicate melts (NSx) of varying sodium concentration. Using only the
partial static structure factors from the MD as an input, MCT reproduces the
large separation in relaxation time scales of the sodium and the silicon/oxygen
components. This confirms the idea of sodium diffusion channels which are
reflected by a prepeak in the static structure factors around 0.95 A^-1, and
shows that it is possible to explain the fast sodium-ion dynamics peculiar to
these mixtures using a microscopic theory.
