The energy above the convex hull E h for a crystal structure 𝑆 𝐶 within the chemical space C is a standard indicator of crystal thermodynamic stability of 𝑆 𝐶 , where C is defined by a set of atomic symbols, and 𝑆 𝐶 is one of the structures that belong to the chemical space C. The quantity E h establishes whether 𝑆 𝐶 could possibly exist, without any indication of how 𝑆 𝐶 might be synthesised. Although it is not the sole determinant of stability of 𝑆 𝐶 , it is a key stability indicator. To evaluate E h for a crystal structure 𝑆 𝐶 within C, one must first enumerate all the crystal phases with energies lower than any other phase with compositions 𝐶 𝑖 that are subsets of C. The phases 𝑆 0 𝐶 𝑖 lie along the convex hull, as shown in Figure ;