Ab initio screening of two-dimensional Cu Q x and Ag Q x chalcogenides.

Two-dimensional (2D) chalcogenides have attracted great interest from the scientific community due to their intrinsic physical-chemical properties, which are suitable for several technological applications. However, most of the reported studies focused on particular compounds and composition, e.g., MoS 2 , MoSe 2 , WS 2 , and WSe 2 . Thus, there is an increased interest to extend our knowledge on 2D chalcogenides. Here, we report a density functional theory (DFT) screening of 2D coinage-metal chalcogenides ( MQ x ), where M = Cu, Ag, Q = S, Se, Te, x = 0.5, 1.0, 1.5, 2.0, with the aim to improve our atomistic understanding of the physical-chemical properties as a function of cation ( M ), anion ( Q ), and composition ( x ). Based on 258 DFT calculations, we selected a set of 22 stable MQ x monolayers based on phonons analyses, where we identified 9 semiconductors (7 AgQ x and 2 CuQ x ), with band gaps from 0.07 eV up to 1.67 eV, while the remaining systems have a metallic character. Using all 258 systems, we found a logarithmic correlation between the average weighted bond lengths and effective coordination number of cations and anions. As expected, the monolayer cohesive energies increase with the radius of the Q species (i.e., from S to Te). Furthermore, an increase in the anion size diminishes the work function for nearly all MQ x monolayers, which can be explained by the nature of the electronic states at the valence band maximum.