Energy Landscape and Electronic Properties of Yttrium Oxysulfide (Y2O2S).

This study investigates the electronic properties and crystalline phases of yttrium oxysulfide (Y2O2S) using theoretical computational methods. A crystal structure prediction was employed to explore the compound's energy landscape. A global optimization using empirical potentials was performed, followed by a local optimization via ab initio calculations using the generalized gradient approximation (GGA), the local density approximation (LDA), and the hybrid B3LYP functional. The computational results confirm the stability of the alpha phase, whose structure aligns with the experimentally observed trigonal modification. Furthermore, four previously unknown metastable polymorphic phases, β-, γ-, δ-, and ε-Y2O2S structures, were identified. An examination of the electronic structure reveals that Y2O2S, a wide-bandgap semiconductor, possesses an indirect energy gap. The results obtained show good agreement with the available literature. A further analysis of the structure-property relationship of the predicted Y2O2S polymorphs indicates the possibility of an indirect-to-direct bandgap transition, which could have significant applications in optoelectronics.