Understanding the Origins of Color Polymorphism from First Principles

Color polymorphism is an intriguing phenomenon, in which different polymorphs of the same molecular solid exhibit different perceived colors. This can result from variations in molecular conformations, diverse crystal packings that lead to varying intermolecular interactions, differing dielectric effects, or a combination of these factors. Here, we use the nonempirical method of the time-dependent (TD) optimally tuned screened range-separated hybrid (OT-SRSH) functional, along with a polarizable continuum model (PCM), to unravel the effect of each factor, based on the well-known example of ROY molecular crystals.