Finally, we used the ∆H f of the compound and its "competing" phases to calculate energy above hull (E hull ) values. Competing phases are those that are closest to a proposed compound by composition. If a competing phase has multiple known polymorphs, we considered every polymorph in our calculations. For our Eu 2+ competing phases, we calculated the total energy with the 4f 7 core pseudopotential and subtracted the Eu (s) energy also calculated with the 4f 7 core pseudopotential to get ∆H f , giving results consistent with published ∆H f values (Table ).