The QHA often gives reasonable predictions of the anharmonic Grüneisen parameter (γ ν = -V ων ∂ων ∂V ) and the thermal expansion in materials -either as a a result of negligible intrinsic anharmonic effects or due to a fortuitous cancellation of errors. The change in unit cell volume can have profound impact on phonon frequencies, and thus the free energy. This can affect the relative stability of different phases or polymorphs and lead to more accurate predictions of stability ranges. Indeed, there are many examples of temperature-driven (first-order) phase transitions that are well described within the QHA, including the monoclinic-to-tetragonal phase transition in ZrO 2 and the α-to-β transition in elemental Sn, through to more complex hybrid organic-inorganic crystals.