Tailoring chemical bonds to design unconventional glasses

Glasses and the corresponding crystals usually share a similar local order and comparable properties. We explain these similarities by quantifying chemical bonding. Using quantum chemical bonding descriptors (electrons transferred and shared between atoms), we demonstrate that in common glasses like SiO2, GeSe2, and GeSe, chemical bonding in the glass and the corresponding crystal hardly differ. To the contrary, for crystals only found in a distinct region of the map, spanned by the two bonding descriptors, unconventional glasses are obtained, which differ in both local order and optical properties. This region contains crystals of GeTe, Sb2Te3, and GeSb2Te4, which employ metavalent bonding. Hence, we can design unconventional glasses by identifying those crystals, which employ theses peculiar bonds