Ab initio Study of Atomic Structure and Electronic Properties of Different Phases of Polymorphic Ag₂S

Silver sulfide is a polymorphic material that exists in different crystalline forms including 3D structures with different symmetries, quasi-2D layers, and 0D quantum dots. The crystal structures of identified and characterized to date forms of Ag₂S differ, and so do their electronic properties. In the past, two different bulk crystalline phases of Ag₂S with the same symmetry have been characterized experimentally. Herein, an empirical relation is proposed, which allows for the identification of these experimentally observed structures of Ag₂S as thermodynamically stable and predicts a new, potentially stable, crystalline phase of this material. The band structures of these three phases are investigated using computational quantum methods. The calculations are performed using the hybrid density functional approximation and quasiparticle partially self-consistent GW method. The effects of crystal structure on the semiconductor properties are discussed based on the results obtained for the three crystalline structures. The findings, reported in this work, can be of significance for technological applications that exploit the electronic properties of crystalline Ag₂S.