Low-Temperature Predicted Structures of Ag₂S (Silver Sulfide)

Silver sulfide phases, such as body-centered cubic argentite and monoclinic acanthite, are widely known. Traditionally, acanthite is regarded as the only low-temperature phase of silver sulfide. However, the possible existence of other low-temperature phases of silver sulfide cannot be ruled out. Until now, there have been only a few suggestions about low-temperature Ag₂S phases that differ from monoclinic acanthite. The lack of a uniform approach has hampered the prediction of such phases. In this work, the use of such an effective tool as an evolutionary algorithm for the first time made it possible to perform a broad search for the model Ag₂S phases of silver sulfide, which are low-temperature with respect to cubic argentite. The possibility of forming Ag₂S phases with cubic, tetragonal, orthorhombic, trigonal, monoclinic, and triclinic symmetry is considered. The calculation of the cohesion energy and the formation enthalpy show, for the first time, that the formation of low-symmetry Ag₂S phases is energetically most favorable. The elastic stiffness constants c of all predicted Ag₂S phases are computed, and their mechanical stability is determined. The densities of the electronic states of the predicted Ag₂S phases are calculated. The prediction of low-temperature Ag₂S structures indicates the possibility of synthesizing new silver sulfide phases with improved properties.