Illustration of the workflow for the construction of coupled interior-atmosphere models with ATHENAIA. For each composition, atmosphere models are calculated with SCARLET (top left) and interior models following D. Thorngren & J. J. Fortney (2019). We couple them with ATHENAIA by finding the R_ref (atmosphere model) and ﹩{T}_{{\rm{mod}}}﹩ (interior model) that minimize δ_TPR (see Equation (5)). The radius at 20 mbar is extracted to construct constant-composition mass–radius curves, while the T–P profile of the envelope is used to evaluate the stability to demixing by comparing to the corresponding H-H₂O coexistence curve (dashed). Finally (right panel), given planetary mass and radius, the range of potential compositions is mapped to f_env − Z_env space (red) and compared to the map of conditions where envelopes are (un)stable against demixing (blue).