(I = Li, Cu, Ag; IV = Si, Ge, Sn; X = S, Se) Chalcogenide Semiconductors*

We present a first-principles investigation, using all-electron hybrid density functional theory, of the chalcogenide semiconductors I₂-II-IV-X₄ (I = Li, Cu, Ag; II = Ba, Sr, Eu, Pb; IV = Si, Ge, Sn; X = S, Se) with the rare-earth (RE) element Eu situated on the II site. Employing these computational approaches and the HSE06 hybrid functional, we examine the validity of a tolerance factor approach developed previously by our team to predict and rationalize the occurrence of different, potentially thermodynamically stable structures, and show agreement between the two approaches in terms of predicting preferred structures. The electronic, optical, and magnetic properties of target compounds were also analyzed using the spin-orbit coupled HSE06 hybrid functional. The description of the Eu 4f states matches benchmark ARPES experiments for Eu-including compounds reported in the literature. Based on the nature of their band structures, as well as band gap values, Cu₂EuGeSe₄, Cu₂EuSnS₄ and Cu₂EuSnSe₄ are identified as potential candidate materials for photovoltaic applications. The compounds are found to be paramagnetic, consistent with experimental results.