Origin of network connectivity and structural units in amorphous SiSe2.

We elucidate the structural properties of amorphous SiSe2 by first-principles molecular dynamics. The calculated structure factor is in very good agreement with experiments, as well as the number of corner- and edge-sharing tetrahedra. By focusing on the sequences of Si atoms linked via intra- and intertetrahedral bonds, we identify the predominant structural motifs. The sequences involving both corner- and edge-sharing connections are significantly more frequent than those formed exclusively by edge-shared Si atoms. Our results clarify a longstanding controversy on the structure of this prototypical disordered network-forming material.