Absence of charge-charge correlations at intermediate-range distances in disordered network-forming materials

Applying a first-principles scheme to liquid GeSe(4), we show that the charge-charge structure factor does not present any feature at the location of the first sharp diffraction peak (FSDP), despite a clear FSDP in the concentration-concentration structure factor S(CC)(k). The origin of this effect is assigned in part to the finite extent of the electron density and in part to electron rearrangements. Our result provides evidence in favor of the postulate that, in binary network-forming systems, charge-charge correlations are absent on intermediate-range length scales. A FSDP in the S(CC)(k) then signals the occurrence of structural defects.