Barium Sulfide under Pressure: Discovery of Metastable Polymorphs and Investigation of Electronic Properties on ab Initio Level

Barium sulfide (BaS) is an important precursor to other barium compounds with applications from ceramics and flame retardants to luminous paints and additives, and recent research shows potential technological applications in electrical and optical devices. Under normal conditions, BaS crystallizes in the NaCl type of structure, and with the increase in pressure BaS undergoes a structural phase transition to a CsCl type modification. This study presents modeling of barium sulfide under pressure with special focus on structural aspects and electronic properties. We predict metastable BaS polymorphs which have not yet been observed in the experiment or in previous calculations, and we investigated their vibrational and thermodynamical properties. Furthermore, we investigate the electronic properties of experimentally known structures as well as novel predicted modifications of BaS on ab initio level using Hartree-Fock, GGA-PBE, and the hybrid B3LYP functional. In this way, we address new possibilities of synthesizing BaS and possible band gap tuning which can have great applications in optoelectrical technologies.