Microscopic origin of concentration fluctuations over intermediate range distances in network-forming disordered systems

Ab initio molecular dynamics simulations of liquid GeSe(2) show that the first sharp diffraction peak in the concentration-concentration structure factor S(CC)(k) is due to a sequence of connected fourfold rings. These subunits can be viewed as chains of edge-sharing tetrahedra. Ge atoms at the opposite tails of these chains are mostly miscoordinated and separated from each other by intermediate range distances. This result correlates a specific structural subunit to a subtle intermediate range order property, involving both the structural and chemical composition of the disordered network.