On four Eu 3+ chemical systems, we compared results from the relativistic pslibrary pseudopotentials (4f 6 frozen-core Eu) to the scalar relativistic SSSP pseudopotentials (4f 6 valence Eu). As a reference demonstrating the impact of using a europium pseudopotential with the wrong number of core 4f electrons, we also relaxed each system using the 4f Calculation results for every proposed and competing structure, as well as a CIF for each relaxed proposed structure, are in the Supporting Information. Several proposed structures were predicted to be stable. They are listed in Table with their energy relative to the convex hull if it were constructed without them (E rel ), and their crystal structures are shown in the Supporting Information.