The vibrational contribution to the free energy is important for quantitative-or even qualitative-prediction of phase diagrams in several cases ranging from metallic alloys , ionic solid solutions , and covalent solid solutions to complex hybrid organic-inorganic materials , and high entropy alloys and compounds . Vibrational free energy can either stabilise or destabilise the formation of solid solutions depending on the sign of ∆S vib , and it may furthermore have effects on the short-range order and physical properties.