First-Principles Prediction of Phonon-Mediated Infrared Optical Properties of WO${}_3$ Polymorphs

Many crystals exhibit polymorphism, undergoing atomic rearrangements that result in unit cells belonging to different symmetry groups. These structural changes directly affect lattice vibration modes and consequently influence their mid-infrared optical properties. In this study, we use tungsten trioxide (WO${}_3$) as a representative system, owing to its multiple temperature-dependent phases, to study the impact of polymorphism on mid-infrared optical behaviour. Using a fully first-principles approach, we investigate three phases of WO${}_3$ and evaluate their mid-infrared optical properties. Significant differences are observed among the three crystallographic phases, demonstrating the potential of this methodology as a predictive tool for materials discovery and targeted design.