  We study the vibrational and electronic properties of (x)Na$_2$S-(1-x)GeS$_2$
glasses through DFT-based molecular dynamics simulations, at different sodium
concentrations ($0<x<0.5$). We compute the vibrational density of states for
the different samples in order to determine the contribution of the Na$^+$ ions
in the VDOS. With an in-depth analysis of the eigenvectors we determine the
spatial and atomic localization of the different modes, and in particular in
the zone corresponding to the Boson peak. We also calculate the electronic
density of states as well as the partial EDOS in order to determine the impact
of the introduction of the sodium modifiers on the electronic properties of the
GeS$_2$ matrix.
