In the second approach, we calculated the free energies of the two lattices by summing the attractive and repulsive interaction energies between the constituent NPs (the interparticle interaction energies were determined from atomistic MD simulations and up/downscaled according to the NP size; for further details on this hybrid approach, see Supplementary Section 6.2). The resulting free-energy maps are shown in Supplementary Fig. ; these results were then integrated onto a single phase diagram (Fig. ), where the regions showing the favorable existence of the CsCl-type and the Th3P4-type lattices are highlighted in green and orange, respectively; a reasonable agreement with the experimental data points can be seen.